JP2023070093A - Flame-retardant nonaqueous electrolytic solution and secondary battery using the same - Google Patents

Abstract

To provide a flame-retardant nonaqueous electrolytic solution that exhibits satisfactory flame retardancy and is also excellent in cycle characteristics and electric resistance characteristics, and to provide a secondary battery using the same.SOLUTION: The flame-retardant nonaqueous electrolytic solution includes at least a nonaqueous solvent and an electrolyte that dissolves in the nonaqueous solvent. The nonaqueous solvent includes at least one of three groups of the following phosphate esters (1) to (3): (1) triethyl phosphate, trimethyl phosphate, tributyl phosphate, and the like; (2) dimethyl monofluorophosphate, diethyl monofluorophosphate, and the like; and (3) methyl difluorophosphate, diethyl difluorophosphate, and the like. The electrolyte includes at least one of a difluorophosphate and a nitrate. A content of the phosphate ester is 20% by mass or more with respect to a total mass of the flame-retardant nonaqueous electrolytic solution.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a flame-retardant non-aqueous electrolyte that exhibits excellent cycle characteristics even after repeated charging and discharging over a long period of time, and a secondary battery using the same.

A conventional lithium-ion secondary battery employs a combustible electrolyte. Therefore, in the charged state, it is in an unstable state in which energy is packed in a flammable electrolytic solution. Therefore, if an abnormality such as an electrical short circuit should occur inside, a fire accident or the like may occur. From this point of view, in the conventional lithium ion secondary battery, it is necessary to ensure safety as a prerequisite for improving the energy density.

Here, from the viewpoint of preventing accidental ignition of lithium ion secondary batteries, it is conceivable to impart flame retardancy and self-extinguishing properties to battery materials, particularly electrolyte solutions. For example, Patent Documents 1 to 3 disclose the use of trialkyl phosphates, which are phosphoric acid esters, as a solvent for electrolytic solutions, or the use of trialkyl phosphates by adding them to conventional electrolytic solutions. With the electrolytic solution disclosed in these patent documents, although the safety of the secondary battery can be improved by imparting flame retardancy to the electrolytic solution, the type of trialkyl phosphate used and the Battery characteristics such as coulombic efficiency were not satisfactory depending on the amount used.

One of the reasons for the deterioration of the battery characteristics of the secondary battery is that the electrolyte used is exposed to an electrochemically strong oxidation-reduction atmosphere, resulting in deterioration of the phosphate ester. Therefore, it is conceivable to use other compounds in combination with the phosphate esters to form a stable film on the surface of the electrode to suppress deterioration of the electrolytic solution.

For example, in Patent Document 4, a carboxylic acid ester is added to the electrolytic solution in addition to the phosphoric acid esters. Further, in Patent Documents 5 and 6, a carbonate having an unsaturated bond is electrolyzed, in Patent Document 7, a halogenated alkoxybenzene, in Patent Document 8, a cyclic phosphate, and in Patent Document 9, a halogenated alkyl phosphate is electrolyzed. Add each to the liquid.

However, the electrolytic solution disclosed in these patent documents causes another problem that the electrical resistance during charging and discharging increases due to the formation of a stable film on the surface of the electrode.

JP-A-4-184870 JP-A-7-114940 Japanese Patent Application Laid-Open No. 2001-307768 JP-A-8-88023 JP-A-11-260401 JP-A-2002-203597 JP-A-11-40193 JP-A-2002-184459 Japanese Patent Application Laid-Open No. 2007-141760

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a flame-retardant non-aqueous electrolytic solution exhibiting good flame retardancy, excellent in cycle characteristics and electrical resistance characteristics, and a secondary electrolyte using the same. It is to provide a battery.

In the present invention, when at least one of a difluorophosphate and a nitrate is used as an electrolyte and a specific phosphate is used as a non-aqueous solvent, the difluorophosphate and the nitrate are highly concentrated in the specific phosphate. and when this solution is used as an electrolytic solution, it exhibits good flame retardancy and exhibits excellent cycle characteristics and electrical resistance characteristics.

That is, the flame-retardant non-aqueous electrolyte according to the present invention is a flame-retardant non-aqueous electrolyte containing at least a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent. The non-aqueous solvent contains at least one of phosphate esters represented by the following chemical formulas (1) to (3), and the electrolyte contains at least one of difluorophosphate and nitrate. and the content of the phosphate ester is 20% by mass or more with respect to the total mass of the flame-retardant non-aqueous electrolyte.

(wherein X ¹ to X ³ are each independently a hydrocarbon group having 1 to 20 carbon atoms; a silyl group having 1 to 20 carbon atoms; a range of 1 to 20 carbon atoms and a halogen atom; , a hydrocarbon group having at least one of hetero atoms or unsaturated bonds; Alternatively, X ¹ to X ³ are a hydrocarbon group having 1 to 20 carbon atoms; a silyl group having 1 to 20 carbon atoms; a hydrocarbon group having at least one of a halogen atom, a heteroatom, or an unsaturated bond; or at least one of a halogen atom, a heteroatom, or an unsaturated bond, wherein the number of carbon atoms is in the range of 1 to 20 , any combination of which are combined together to form a cyclic structure. Y ¹ and Y ² each independently represent a halogen atom.)

In the above structure, the molar fraction of at least one of the difluorophosphate and the nitrate is preferably 0.1 or more with respect to the total number of moles of the electrolyte.

Further, in the above constitution, at least one of the difluorophosphate and the nitrate is preferably an alkali metal salt.

Furthermore, in the above configuration, at least one of the difluorophosphate and nitrate is preferably a lithium salt.

In the above structure, the phosphate ester is trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, diethyl monofluorophosphate, diethyl monofluorophosphate, ethyl difluorophosphate, dichlorophosphate. Ethyl and diethyl (2-(2-(2-methoxyethoxy)ethoxy)ethyl phosphate) are preferred.

In the above configuration, at least one other electrolyte having an anion of BF ₄ ⁻ , PF ₆ ⁻ , N(CF ₃ SO ₂ ) ₂ ⁻ or N(SO ₂ F) ₂ ⁻ is used as the electrolyte. It is preferable to further include.

In the above configuration, the non-aqueous solvent comprises a cyclic carbonate, a chain carbonate, a cyclic ether, a chain ether, a lactone compound, a chain ester, a nitrile compound, an amide compound, a sulfone compound, and a sulfoxide compound. It is preferable to further include at least one selected from the group.

In the above configuration, the non-aqueous solvent preferably further contains at least one of propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethylsulfoxide and tetraethylene glycol dimethyl ether.

A secondary battery according to the present invention includes at least a flame-retardant non-aqueous electrolyte, a positive electrode, and a negative electrode in order to solve the above-described problems.

According to the present invention, by using a non-aqueous solvent containing at least one of the phosphate esters represented by the chemical formulas (1) to (3), the flame-retardant can be improved. In addition, by containing at least one of difluorophosphate and nitrate dissolved in a non-aqueous solvent containing the phosphate ester as an electrolyte, the electrodes (positive electrode and negative electrode) after repeated charging and discharging A flame-retardant non-aqueous electrolyte that suppresses an increase in electrical resistance, maintains a good capacity retention rate even after repeated charging and discharging over a long period of time, and has excellent cycle characteristics, and a secondary battery using the same. can provide.

Although the mechanism by which the cycle characteristics and electrical resistance characteristics are improved is not clear, at least one of difluorophosphate and nitrate contained as an electrolyte forms a good coating on the surface of the electrode (electrode active material layer). prevents the electrolytic solution from being exposed to an electrochemically strong oxidation-reduction atmosphere. It is believed that this suppresses deterioration of the phosphate ester in the electrolytic solution, and suppresses or improves deterioration in cycle characteristics and electrical resistance characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram which shows the outline of the non-aqueous secondary battery which concerns on one Embodiment of this invention.

(Flame-retardant non-aqueous electrolyte)
The flame-retardant non-aqueous electrolyte (hereinafter referred to as "non-aqueous electrolyte") according to the present embodiment contains at least a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent, and is used for lithium ion secondary batteries and the like. can be suitably used as an electrolyte for a secondary battery.

As the non-aqueous solvent, one containing at least one of the phosphate esters represented by the following chemical formulas (1) to (3) (hereinafter sometimes collectively referred to as "phosphate ester") is used. . As the electrolyte, one containing at least one of difluorophosphate and nitrate is used.

During initial charging, an irreversible reaction of decomposition of the non-aqueous electrolyte occurs at the interface between the electrode and the non-aqueous electrolyte. Electrode active material, types of non-aqueous solvents and electrolytes in the non-aqueous electrolyte and additives added as necessary, properties of the film formed according to charge and discharge conditions, such as thermal stability and ionic conductivity, Properties such as morphology and density are expected to vary greatly. In the present embodiment, a phosphate ester is used as the non-aqueous solvent, and at least one of difluorophosphate and nitrate is used as the electrolyte, thereby forming an effective film on the surface of the electrode (electrode active material layer). Due to the properties of this film, it is believed that the cycle characteristics and electrical resistance characteristics of the secondary battery are improved. Moreover, sufficient flame retardancy can be imparted to the non-aqueous electrolyte by using the phosphate ester as the non-aqueous solvent.

<Non-aqueous solvent>
[Phosphate ester]
As described above, the non-aqueous solvent contains at least one of the phosphate esters represented by the following chemical formulas (1) to (3).

In chemical formulas (1) to (3), X ¹ to X ³ are each independently a hydrocarbon group; a silyl group; a hydrocarbon group having at least one of a halogen atom, a heteroatom or an unsaturated bond; (hereinafter referred to as "a hydrocarbon group having a halogen atom etc."); or a silyl group having at least one of a halogen atom, a hetero atom or an unsaturated bond (hereinafter referred to as a "silyl group having a halogen atom etc.") ). Alternatively, X ¹ to X ³ are a hydrocarbon group having 1 to 20 carbon atoms; a silyl group having 1 to 20 carbon atoms; or a hydrocarbon group having at least one unsaturated bond; or a silyl group having at least one of a halogen atom, a heteroatom, or an unsaturated bond, wherein the number of carbon atoms is in the range of 1 to 20 , any combination of which are combined together to form a cyclic structure.

The number of carbon atoms of the hydrocarbon group in X ¹ to X ³ is 1 to 20, preferably 1 to 10, more preferably 1 to 4. In this specification, when a range of carbon number is expressed, the range means to include all integer carbon numbers included in the range. Therefore, for example, a “hydrocarbon group having 1 to 3 carbon atoms” means all hydrocarbon groups having 1, 2 and 3 carbon atoms.

The number of carbon atoms of the silyl groups in X ¹ to X ³ is 1 to 20, preferably 1 to 10, more preferably 1 to 4.

The hydrocarbon group having a halogen atom in X ¹ to X ³ means a functional group in which some or all of the hydrogen atoms in the hydrocarbon group are substituted with halogen atoms. Halogen atoms include atoms of fluorine, chlorine, bromine, and iodine. In the hydrocarbon group having a halogen atom having 1 to 20 carbon atoms, a hydrocarbon group having a halogen atom having 1 to 10 carbon atoms is preferable, and a hydrocarbon group having a halogen atom having 1 to 4 carbon atoms groups are more preferred.

The heteroatom-containing hydrocarbon group for X ¹ to X ³ above means a functional group in which some or all of the hydrogen atoms and carbon atoms in the hydrocarbon group are replaced with heteroatoms. Said heteroatoms represent atoms such as oxygen, nitrogen and sulfur. Hydrocarbon groups having a heteroatom of 1 to 20 carbon atoms are preferably hydrocarbon groups having a heteroatom of 1 to 10 carbon atoms, and hydrocarbon groups having a heteroatom of 1 to 4 carbon atoms. is more preferred.

The hydrocarbon group having an unsaturated bond in X ¹ to X ³ means, for example, a hydrocarbon group having a carbon-carbon double bond or triple bond. The number of unsaturated bonds is preferably in the range of 1-10, more preferably in the range of 1-5, and particularly preferably in the range of 1-3.

The silyl group having a halogen atom in X ¹ to X ³ means a functional group in which some or all of the hydrogen atoms in the silyl group are substituted with halogen atoms. Halogen atoms include atoms of fluorine, chlorine, bromine, and iodine. In the silyl group having a halogen atom having 1 to 20 carbon atoms, a silyl group having a halogen atom having 1 to 10 carbon atoms is preferable, and a silyl group having a halogen atom having 1 to 4 carbon atoms is more preferable. preferable.

The heteroatom-containing silyl group in X ¹ to X ³ above means a functional group in which some or all of the hydrogen atoms and carbon atoms in the silyl group are replaced with heteroatoms. Said heteroatoms represent atoms such as oxygen, nitrogen and sulfur. Among silyl groups having a heteroatom of 1 to 20 carbon atoms, silyl groups having a heteroatom of 1 to 10 carbon atoms are preferred, and silyl groups having a heteroatom of 1 to 4 carbon atoms are more preferred. .

The silyl group having an unsaturated bond in X ¹ to X ³ means, for example, a silyl group having a carbon-carbon double bond or triple bond. The number of unsaturated bonds is preferably in the range of 1-10, more preferably in the range of 1-5, and particularly preferably in the range of 1-3.

The hydrocarbon group and the hydrocarbon group having a halogen atom or the like are not particularly limited, and examples thereof include a methyl group, an ethyl group, a propyl group, a butyl group, an isopropyl group, a pentyl group, a hexyl group, a heptyl group and an octyl group. A chain alkyl group, a cyclic alkyl group such as a cyclopentyl group and a cyclohexyl group; 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group, 1,2-diiodoethyl group, 1,2-dibromo ethyl group, 1,2-dichloroethyl group, 1,2-difluoroethyl group, 2,2-diiodoethyl group, 2,2-dibromoethyl group, 2,2-dichloroethyl group, 2,2-difluoroethyl group, Chain halogen-containing alkyl groups such as 2,2,2-tribromoethyl group, 2,2,2-trichloroethyl group, 2,2,2-trifluoroethyl group and hexafluoro-2-propyl group: 2- Cyclic halogen-containing alkyl groups such as iodocyclohexyl group, 2-bromocyclohexyl group, 2-chlorocyclohexyl group and 2-fluorocyclohexyl group; chains such as 2-propenyl group, isopropenyl group, 2-butenyl group and 3-butenyl group Cyclic alkenyl group; cyclic alkenyl group such as 2-cyclopentenyl group, 2-cyclohexenyl group and 3-cyclohexenyl group; 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl chain alkynyl groups such as groups, 2-pentynyl groups, 3-pentynyl groups and 4-pentynyl groups; aryl groups such as phenyl groups; 3-methoxyphenyl groups, 4-methoxyphenyl groups, 3,5-dimethoxyphenyl groups and Alkoxyphenyl groups such as 4-phenoxyphenyl group; 2-iodophenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group , 3-fluorophenyl group, 4-iodophenyl group, 4-bromophenyl group, 4-chlorophenyl group, 4-fluorophenyl group, 3,5-diiodophenyl group, 3,5-dibromophenyl group, 3,5 -Halogen-containing phenyl groups such as a dichlorophenyl group and a 3,5-difluorophenyl group; naphthyl groups such as a 1-naphthyl group, a 2-naphthyl group and a 3-amino-2-naphthyl group; a 2-methoxyethyl group, 2-( 2-methoxyethoxy)ethyl group, 2-(2-(2-methoxyethoxy)ethoxy)ethyl group and 2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl group and the like.

In chemical formulas (2) and (3), ^Y1 and ^Y2 each independently represent a halogen atom. Halogen atoms include atoms of fluorine, chlorine, bromine, and iodine.

Specific examples of the phosphate represented by the chemical formula (1) include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triphenyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, methyldipropyl phosphate, dimethylpropyl phosphate, butylmethyl phosphate, dibutylmethyl phosphate, dimethylpentyl phosphate, methyldipentyl phosphate, hexyldimethyl phosphate, dihexylmethyl phosphate, Diheptyl methyl phosphate, heptyl dimethyl phosphate, ethyl dipropyl phosphate, diethyl propyl phosphate, butyl diethyl phosphate, dibutyl ethyl phosphate, ethyl dipentyl phosphate, diethyl pentyl phosphate, ethyl dihexyl phosphate, di phosphate Ethylhexyl, Ethylheptyl Phosphate, Diethylheptyl Phosphate, Butyl Dipropyl Phosphate, Dibutylpropyl Phosphate, Butyl Dipentyl Phosphate, Dibutyl Pentyl Phosphate, Butyl Dihexyl Phosphate, Dibutyl Hexyl Phosphate, Butyl Diheptyl Phosphate, Phosphorus dibutylheptyl acid, hexylpentyl phosphate, dihexylpentyl phosphate, heptylpentyl phosphate, diheptylpentyl phosphate, diheptylhexyl phosphate, heptyldihexyl phosphate, ethyl methyl propyl phosphate, ethyl methyl butyl phosphate, phosphoric acid ethyl methyl pentyl, ethylhexylmethyl phosphate, ethylheptylmethyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(2,2,2-trichloroethyl) phosphate, tris(2, 2,2-tribromoethyl), tris(2,2,2-triiodoethyl) phosphate, tris(1,1,1,3,3,3-hexafluoroisopropyl) phosphate, tris(1 , 1,1,3,3,3-hexachloroisopropyl), tris(1,1,1,3,3,3-hexabromoisopropyl) phosphate, tris(1,1,1,3,3, 3-hexaiodoisopropyl), (2,2,2-trifluoroethyl)diethyl phosphate, bis(2,2,2-trifluoroethyl)ethyl phosphate, (1,1,1,3,3 ,3-hexafluoroisopropyl)diethyl, bis(1,1,1,3,3,3-hexafluoroisopropyl)ethyl phosphate, tris(2-methoxyethyl) phosphate, tris(2-(2- methoxyethoxy)ethyl), phosphoric acid, tris(2-(2-(2-methoxyethoxy)ethoxy)ethyl) phosphate, tris phosphate, tris(2-(2-(2-(2-methoxyethoxy) )ethoxy)ethoxy)ethyl), diethyl phosphate (2-methoxyethyl), diethyl phosphate (2-(2-methoxyethoxy)ethyl), diethyl phosphate (2-(2-(2-methoxyethoxy)ethoxy) ethyl), diethyl phosphate (2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl), ethyl bis(2-methoxyethyl) phosphate, ethyl bis(2-(2-methoxyethoxy) phosphate ethyl), ethyl bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl) phosphate, ethyl bis(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl) phosphate, phosphoric acid tris(trimethylsilyl), tris(trimethylbutyl) phosphate, tris(triphenylsilyl) phosphate, tris(dimethylphenylsilyl) phosphate, tris(dimethylvinylsilyl) phosphate, and the like. These phosphate esters can be used alone or in combination of two or more.

Further, among the phosphate esters represented by the exemplified chemical formula (1), trimethyl phosphate, triethyl phosphate, triisopropyl phosphate and tributyl phosphate are preferable from the viewpoint of availability, and trimethyl phosphate, Triethyl phosphate and tributyl phosphate are more preferred, triethyl phosphate and trimethyl phosphate are more preferred, and triethyl phosphate is particularly preferred.

Specific examples of the phosphate represented by the chemical formula (2) include dimethyl monofluorophosphate, diethyl monofluorophosphate, dipropyl monofluorophosphate, diisopropyl monofluorophosphate, dibutyl monofluorophosphate, dipentyl monofluorophosphate, diheptyl monofluorophosphate, bis(2,2,2-trifluoroethyl) monofluorophosphate, bis(1,1,1,3,3,3-hexafluoroisopropyl monofluorophosphate) ), bis(2-methoxyethyl) monofluorophosphate, bis(2-(2-methoxyethoxy)ethyl) monofluorophosphate, bis(2-(2-(2-methoxyethoxy)ethoxy) monofluorophosphate ethyl), bis(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl) monofluorophosphate, dimethyl monophosphate, diethyl monophosphate, dipropyl monophosphate, diisopropyl monophosphate, dibutyl monophosphate, dipentyl monophosphate, diheptyl monophosphate, bis(2,2,2-trifluoroethyl)monomonophosphate, bis(1,1,1,3,3,3-hexafluoro)monophosphate isopropyl), bis(2-methoxyethyl) monophosphate, bis(2-(2-methoxyethoxy)ethyl) monophosphate, bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)monophosphate , Monobromophosphate bis(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl), dimethyl monobromophosphate, diethyl monobromophosphate, dipropyl monobromophosphate, diisopropyl monobromophosphate, dibutyl monobromophosphate, dipentyl monobromophosphate , diheptyl monobromophosphate, bis(2,2,2-trifluoroethyl) monobromophosphate, bis(1,1,1,3,3,3-hexafluoroisopropyl) monobromophosphate, bis(2-methoxyethyl) monobromophosphate , bis(2-(2-methoxyethoxy)ethyl)monobromophosphate, bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)monobromophosphate, bis(2-(2-(2-(2 -methoxyethoxy)ethoxy)ethoxy)ethyl), dimethyl monoiodrate, diethyl monoiodrate, dipropyl monoiodrate, diisopropyl monoiodrate, dibutyl monoiodrate, dipentyl monoiodrate, diheptyl monoiodrate, bis(2,2,2-tri-monoiodrate) fluoroethyl), bis(1,1,1,3,3,3-hexafluoroisopropyl)monoiophosphate, bis(2-methoxyethyl)monoiophosphate, bis(2-(2-methoxyethoxy)ethyl)monoiophosphate, Bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)monoiophosphate, Bis(2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl)monoiophosphate, Bismonofluorophosphate (trimethylsilyl), bis(trimethylsilyl) monobromophosphate, bis(trimethylsilyl) monobromophosphate, bis(trimethylsilyl) iodophosphate, bis(triethylsilyl) monofluorophosphate, bis(triethylsilyl) monobromophosphate, bis(triethyl monobromophosphate) silyl), bis(triethylsilyl) monoiophosphate, bis(dimethylphenylsilyl) monofluorophosphate, bis(dimethylphenylsilyl) monomonophosphate, bis(dimethylphenylsilyl) monobromophosphate, bis(dimethylphenylsilyl) monoiophosphate, bis(dimethylvinylsilyl) monofluorophosphate, bis(dimethylvinylsilyl) monomonophosphate, bis(dimethylvinylsilyl) monobromophosphate, bis(dimethylvinylsilyl) monoiodophosphate and the like. These phosphate esters can be used alone or in combination of two or more.

Further, among the phosphate esters represented by the exemplified chemical formula (2), from the viewpoint of availability and electrochemical stability, dimethyl monophosphate, diethyl monofluorophosphate, dimethyl monofluorophosphate, mono Diethyl fluorophosphate is preferred, and dimethyl monofluorophosphate and diethyl monofluorophosphate are more preferred.

Specific examples of the phosphate represented by the chemical formula (3) include methyl difluorophosphate, ethyl difluorophosphate, propyl difluorophosphate, isopropyl difluorophosphate, butyl difluorophosphate, pentyl difluorophosphate, Hexyl difluorophosphate, heptyl difluorophosphate, difluorophosphate (2,2,2-trifluoroethyl), difluorophosphate (1,1,1,3,3,3-hexafluoroisopropyl), difluorophosphate ( 2-methoxyethyl), difluorophosphate (2-(2-methoxyethoxy)ethyl), difluorophosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), difluorophosphate (2-(2- (2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl), methyl dichlorophosphate, ethyl dichlorophosphate, propyl dichlorophosphate, isopropyl dichlorophosphate, butyl dichlorophosphate, pentyl dichlorophosphate, hexyl dichlorophosphate , heptyl dichlorophosphate, dichlorophosphate (2,2,2-trifluoroethyl), dichlorophosphate (1,1,1,3,3,3-hexafluoroisopropyl), difluorophosphate (2-methoxyethyl) ), dichlorophosphate (2-(2-methoxyethoxy)ethyl), dichlorophosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), dichlorophosphate (2-(2-(2-( 2-methoxyethoxy)ethoxy)ethoxy)ethyl), methyl dibromophosphate, ethyl dibromophosphate, propyl dibromophosphate, isopropyl dibromophosphate, butyl dibromophosphate, pentyl dibromophosphate, hexyl dibromophosphate, dibromoline heptyl acid, dibromophosphate (2,2,2-trifluoroethyl), dibromophosphate (1,1,1,3,3,3-hexafluoroisopropyl), dibromophosphate (2-methoxyethyl), dibromo Phosphate (2-(2-methoxyethoxy)ethyl), dibromophosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), dibromophosphate (2-(2-(2-(2-methoxy) ethoxy)ethoxy)ethoxy)ethyl), methyl diiophosphate, ethyl diiophosphate, propyl diiophosphate, isopropyl diiophosphate, butyl diiophosphate, pentyl diiophosphate, hexyl diiophosphate, heptyl diiophosphate, diiophosphate (2,2,2- trifluoroethyl), diiophosphate (1,1,1,3,3,3-hexafluoroisopropyl), diiophosphate (2-methoxyethyl), diiophosphate (2-(2-methoxyethoxy)ethyl), diiophosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), diiophosphate (2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl), methyl chlorofluorophosphate, chlorofluorophosphorus Ethyl acid, propyl chlorofluorophosphate, isopropyl chlorofluorophosphate, pentyl chlorofluorophosphate, hexyl chlorofluorophosphate, heptyl chlorofluorophosphate, (2,2,2-trifluoroethyl) chlorofluorophosphate, chloro Fluorophosphate (1,1,1,3,3,3-hexafluoroisopropyl), Chlorofluorophosphate (2-methoxyethyl), Chlorofluorophosphate (2-(2-methoxyethoxy)ethyl), Chlorofluoro Phosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), chlorofluorophosphate (2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl), methyl bromochlorophosphate , ethyl bromofluorophosphate, propyl bromofluorophosphate, isopropyl bromofluorophosphate, pentyl bromofluorophosphate, hexyl bromofluorophosphate, heptyl bromofluorophosphate, bromofluorophosphate (2,2,2-trifluoro ethyl), bromofluorophosphate (1,1,1,3,3,3-hexafluoroisopropyl), bromofluorophosphate (2-methoxyethyl), bromofluorophosphate (2-(2-methoxyethoxy)ethyl) ), bromofluorophosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), bromofluorophosphate (2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)ethyl), fluoro methyl iodinate, ethyl fluoroiodrate, propyl fluoroiodrate, isopropyl fluoroiodrate, pentyl fluoroiodrate, hexyl fluoroiodrate, heptyl fluoroiodrate, fluoroiodphosphate (2,2, 2-trifluoroethyl), fluoroiodophosphate (1,1,1,3,3,3-hexafluoroisopropyl), fluoroiodophosphate (2-methoxyethyl), chlorofluorophosphate (2-(2- methoxyethoxy)ethyl), fluoroiophosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), fluoroiophosphate (2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy) ethyl), methyl bromochlorophosphate, ethyl bromochlorophosphate, propyl bromochlorophosphate, isopropyl bromochlorophosphate, pentyl bromochlorophosphate, hexyl bromochlorophosphate, heptyl bromochlorophosphate, bromochlorophosphate ( 2,2,2-trifluoroethyl), bromochlorophosphate (1,1,1,3,3,3-hexafluoroisopropyl), bromochlorophosphate (2-methoxyethyl), bromochlorophosphate (2 -(2-methoxyethoxy)ethyl), bromochlorophosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl), bromochlorophosphate (2-(2-(2-(2-methoxyethoxy) ethoxy)ethoxy)ethyl), methyl chloroiodinate, ethyl chloroiodinate, propyl chloroiodinate, isopropyl chloroiodinate, pentyl chloroiodrate, hexyl chloroiodinate, heptyl chloroiodinate, chloro Iodophosphate (2,2,2-trifluoroethyl), Chloriodophosphate (1,1,1,3,3,3-hexafluoroisopropyl), Chloriodophosphate (2-methoxyethyl), Chlorofluoro (2-(2-Methoxyethoxy)ethyl) phosphate, (2-(2-(2-methoxyethoxy)ethoxy)ethyl chloroiophosphate), (2-(2-(2-(2 -methoxyethoxy)ethoxy)ethoxy)ethyl, trimethylsilyl difluorophosphate, trimethylsilyl dichlorophosphate, trimethylsilyl dibromophosphate, trimethylsilyl diiophosphate, triethylsilyl difluorophosphate, triethylsilyl dichlorophosphate, triethylsilyl dibromophosphate, triethyl diiophosphate Silyl, dimethylphenylsilyl difluorophosphate, dimethylphenylsilyl dichlorophosphate, dimethylphenylsilyl dibromophosphate, dimethylphenylsilyl diiophosphate, dimethylvinylsilyl difluorophosphate, dimethylvinylsilyl dichlorophosphate, dimethylvinylsilyl dibromophosphate, Dimethylvinylsilyl diiophosphate, trimethylsilyl fluorochlorophosphate, trimethylsilyl fluorobromophosphate, trimethylsilyl fluoroiophosphate, triethylsilyl fluorochlorophosphate, triethylsilyl fluorobromophosphate, and triethylsilyl fluoroiophosphate. These phosphate esters can be used alone or in combination of two or more.

Among the phosphate esters represented by the chemical formula (3), methyl dichlorophosphate, ethyl dichlorophosphate, methyl difluorophosphate, and difluorophosphorus are preferred from the standpoint of availability and electrochemical stability. Diethyl acid is preferred, and methyl difluorophosphate and diethyl difluorophosphate are more preferred.

The content of the phosphate ester is 20% by mass or more, preferably 20% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 80% by mass or less, relative to the total mass of the non-aqueous electrolyte. More preferably, it is 40% by mass or more and 70% by mass or less. By setting the content of the phosphate ester within these ranges, good flame retardancy can be imparted to the non-aqueous electrolyte.

[Other non-aqueous solvents]
The non-aqueous solvent may contain other non-aqueous solvents in addition to the phosphate ester. Other non-aqueous solvents are not particularly limited, and examples include cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, lactone compounds, chain esters, nitrile compounds, amide compounds, sulfone compounds, sulfoxide compounds, and the like. mentioned. These other non-aqueous solvents can be used alone or in combination of two or more. Further, among these other non-aqueous solvents, carbonate esters are preferable from the viewpoint of enabling general use as a non-aqueous solvent for secondary batteries.

The cyclic carbonate is not particularly limited, and examples thereof include ethylene carbonate, propylene carbonate, and butylene carbonate. These cyclic carbonates can be used singly or in combination of two or more.

The chain carbonate is not particularly limited, and examples thereof include dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate and the like. These chain carbonate esters can be used singly or in combination of two or more.

The cyclic ether is not particularly limited and includes, for example, tetrahydrofuran, 2-methyltetrahydrofuran and the like. These cyclic ethers can be used singly or in combination of two or more.

The chain ether is not particularly limited, and examples thereof include dimethoxyethane, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and the like. These chain ethers can be used singly or in combination of two or more.

The lactone compound is not particularly limited, and examples thereof include γ-butyrolactone.

The chain ester is not particularly limited, and examples thereof include methyl propionate, methyl acetate, ethyl acetate, methyl formate and the like. These chain esters can be used singly or in combination of two or more.

The nitrile compound is not particularly limited, and examples thereof include acetonitrile.

The amide compound is not particularly limited, and examples thereof include dimethylformamide.

The sulfone compound is not particularly limited, and examples thereof include sulfolane and methylsulfolane. These sulfone compounds can be used singly or in combination of two or more.

In other non-aqueous solvents, those in which at least part of the hydrogen atoms of the hydrocarbon groups contained in the molecule are substituted with fluorine atoms can also be preferably used.

Among other exemplified non-aqueous solvents, propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl sulfoxide, and tetraethylene glycol dimethyl ether are preferable from the standpoint of availability and improvement of secondary battery performance. Moreover, from the viewpoint of improving the charging efficiency of the secondary battery, cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonate esters such as dimethyl carbonate and ethylmethyl carbonate are preferable.

<Electrolyte>
[Difluorophosphate and nitrate]
As described above, the electrolyte contains at least one of difluorophosphate and nitrate. Difluorophosphates and nitrates preferably exhibit solubility in phosphoric acid esters. As used herein, the term "solubility" means that 0.05 g or more of difluorophosphate and/or nitrate dissolves in 100 g of a non-aqueous solvent at 25°C, for example.

From the viewpoint of solubility in non-aqueous solvents and secondary battery properties, difluorophosphates and nitrates having alkali metal ions as cations are preferred. Alkali metal ions include, for example, lithium ions, sodium ions, potassium ions, rubidium ions, and cesium ions. Of these alkali metal ions, lithium ions, sodium ions, and potassium ions are preferred from the viewpoint of secondary battery characteristics and resources.

The concentration of the electrolyte in the non-aqueous solvent is preferably in the range of 0.1M to 4M, more preferably in the range of 0.2M to 1.5M, even more preferably in the range of 0.5M to 1.2M. By setting the concentration of the electrolyte to 0.1 M or more, it is possible to prevent the electrical conductivity of the non-aqueous electrolyte from becoming insufficient and the electrical resistance characteristics from deteriorating. On the other hand, by setting the concentration of the electrolyte to 4M or less, the electrolyte reaches the saturation solubility in the nonaqueous solvent, which increases the viscosity of the nonaqueous electrolyte, thereby improving the handling of the nonaqueous electrolyte and the electricity of the secondary battery. It is possible to prevent deterioration of resistance characteristics.

The mole fraction of difluorophosphate and/or nitrate is preferably 0.1 or more, more preferably 0.1 or more and 1.0 or less, and 0.2 or more and 0.8 with respect to the total number of moles of the electrolyte. The following are more preferable, and 0.3 or more and 0.5 or less are particularly preferable. By setting the mole fraction of difluorophosphate and/or nitrate to 0.1 or more, the cycle characteristics and electrical resistance characteristics of the secondary battery can be further improved.

[Other electrolytes]
As described above, electrolytes other than difluorophosphate and nitrate can be used in combination. Other electrolytes are not particularly limited, and examples include PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , C ₂ F ₅ SO ₃ ⁻ , C ₃ F ₇ SO ₃ ⁻ , C ₄ F ₉ SO ^{3 −} , N(SO ₂ F) ₂ ⁻ , N(CF ₃ SO ₂ ) ₂ ⁻ , N(C ₂ F ₅ SO ₂ ) ₂ ⁻ , N(CF ₃ SO ₂ )(CF ₃ CO) ⁻ , N(CF ₃ SO ₂ )(C ₂ F ₅ SO ₂ ) ⁻ , C(CF ₃ SO ₂ ) ₃ ⁻ and other anions, boron complex salts, phosphorus complex salts, Lewis acid complex salts, phosphate ester salts and the like. These other electrolytes can be used singly or in combination of two or more. Other electrolytes are described in further detail below. The mole fraction of the other electrolyte is preferably in the range of 0.1 or more and 0.9 or less, more preferably 0.2 or more and 0.8 or less, and 0.3 with respect to the total number of moles of the electrolyte. A range of 0.5 or less is more preferable. By setting the content within these ranges, the cycle characteristics and electrical resistance characteristics of the secondary battery can be further improved.

1. Boron Complex Salt The boron complex salt is specifically represented by the following chemical formula (4).

In the chemical formula (4), Mn ⁺ represents any one selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions and onium ions.

The alkali metal ion in the chemical formula (4) is not particularly limited, and includes lithium ion, sodium ion, potassium ion, rubidium ion, cesium ion and the like. These can be used singly or in combination of two or more.

Examples of the alkaline earth metal ions in the chemical formula (4) include magnesium ions, calcium ions, strontium ions, barium ions, and the like. These can be used singly or in combination of two or more.

The transition metal ions in the chemical formula (4) are not particularly limited, and examples thereof include manganese ions, cobalt ions, nickel ions, chromium ions, copper ions, silver ions, molybdenum ions, tungsten ions, vanadium ions, and the like. . These can be used singly or in combination of two or more.

The onium ions in the chemical formula (4) include ammonium ions (NH ⁴⁺ ), primary ammonium ions, secondary ammonium ions, tertiary ammonium ions, quaternary ammonium ions, quaternary phosphonium ions, sulfonium ion and the like.

The primary ammonium ion is not particularly limited, and examples thereof include methylammonium ion, ethylammonium ion, propylammonium ion, isopropylammonium ion and the like. These can be used singly or in combination of two or more.

The secondary ammonium ion is not particularly limited, and examples thereof include dimethylammonium ion, diethylammonium ion, dipropylammonium ion, dibutylammonium ion, ethylmethylammonium ion, methylpropylammonium ion, methylbutylammonium ion, and propylbutylammonium ion. ions, diisopropylammonium ions, and the like. These can be used singly or in combination of two or more.

The tertiary ammonium ion is not particularly limited, and examples thereof include trimethylammonium ion, triethylammonium ion, tripropylammonium ion, tributylammonium ion, ethyldimethylammonium ion, diethylmethylammonium ion, triisopropylammonium ion, and dimethylisopropylammonium ion. ion, diethylisopropylammonium ion, dimethylpropylammonium ion, butyldimethylammonium ion, 1-methylpyrrolidinium ion, 1-ethylpyrrolidinium ion, 1-propylpyrrolidinium ion, 1-butylpropylpyrrolidinium ion, 1-methylimidazo Lithium ion, 1-ethylimidazolium ion, 1-propylimidazolium ion, 1-butylimidazolium ion, pyrazolium ion, 1-methylpyrazolium ion, 1-ethylpyrazolium ion, 1-propylpyrazolium ion, 1 -butylpyrazolium ion, pyridinium ion and the like. These can be used singly or in combination of two or more.

The quaternary ammonium forming the quaternary ammonium ion is not particularly limited, and examples thereof include aliphatic quaternary ammoniums, imidazoliums, pyridiniums, pyrazoliums, and pyridaziniums. These can be used singly or in combination of two or more.

Further, the aliphatic quaternary ammonium is not particularly limited, and examples thereof include tetraethylammonium, tetrapropylammonium, tetraisopropylammonium, trimethylethylammonium, dimethyldiethylammonium, methyltriethylammonium, trimethylpropylammonium, trimethylisopropylammonium, tetra butylammonium, trimethylbutylammonium, trimethylpentylammonium, trimethylhexylammonium, 1-ethyl-1-methyl-pyrrolidinium, 1-butyl-1-methylpyrrolidinium, 1-ethyl-1-methyl-piperidinium, 1-butyl- 1-methylpiperidinium and the like. These can be used singly or in combination of two or more.

The imidazoliums are not particularly limited, and examples include 1.3 dimethyl-imidazolium, 1-ethyl-3-methylimidazolium, 1-n-propyl-3-methylimidazolium, 1-n-butyl-3 -methylimidazolium, 1-n-hexyl-3-methylimidazolium, and the like. These can be used singly or in combination of two or more.

The pyridiniums are not particularly limited, and examples thereof include 1-methylpyridinium, 1-ethylpyridinium, 1-n-propylpyridinium and the like. These can be used singly or in combination of two or more.

The pyrazoliums are not particularly limited, and examples include 1,2-dimethylpyrazolium, 1-methyl-2-ethylpyrazolium, 1-propyl-2-methylpyrazolium, 1-methyl-2-butyl pyrazolium, 1-methylpyrazolium, 3-methylpyrazolium, 4-methylpyrazolium, 4-iodopyrazolium, 4-bromopyrazolium, 4-iodo-3-methylpyrazolium, 4-bromo-3-methylpyrazolium and 3-trifluoromethylpyrazolium. These can be used singly or in combination of two or more.

The pyridaziniums are not particularly limited, and examples include 1-methylpyridazinium, 1-ethylpyridazinium, 1-propylpyridazinium, 1-butylpyridazinium, 3-methylpyridazinium. 4-methylpyridazinium, 3-methoxypyridazinium, 3,6-dichloropyridazinium, 3,6-dichloro-4-methylpyridazinium, 3-chloro-6-methylpyridazinium Dazinium, 3-chloro-6-methoxypyridazinium. These can be used singly or in combination of two or more.

The quaternary phosphonium constituting the quaternary phosphonium ion is not particularly limited, and examples thereof include benzyltriphenylphosphonium, tetraethylphosphonium, tetraphenylphosphonium and the like. These can be used singly or in combination of two or more.

The sulfonium forming the sulfonium ion is not particularly limited, and examples thereof include trimethylsulfonium, triphenylsulfonium, triethylsulfonium and the like. These can be used singly or in combination of two or more.

Among those listed as examples of Mn ⁺ , from the viewpoint of availability, lithium ion, sodium ion, potassium ion, magnesium ion, calcium ion, tetraalkylammonium ion, alkylimidazolium ion, alkylpyrrolidinium ion, alkyl Pyridinium ions are preferred.

L ¹ to L ⁴ in the chemical formula (4) are each independent, and one or two arbitrarily selected combinations are -OOC-COO-, -OOC-O-, -OOC-α-COO It represents a ring structure of -, -O-α-O- or -OOC-α-O-. α is a hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms; represents a hydrocarbon group having a heteroatom, an unsaturated bond, or a cyclic structure. When L ¹ to L ⁴ have two sets of any one of -OOC-α-COO-, -O-α-O- or -OOC-α-O-, each α is different good too. Here, a heteroatom means an oxygen atom, a nitrogen atom or a sulfur atom.

The α is not particularly limited, and examples thereof include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a linear alkylene group such as a nonylene group; methylene group, bromomethylene group, dibromomethylene group, fluoromethylene group, difluoromethylene group, iodoethylene group, 1,1-diiodoethylene group, 1,2-diiodoethylene group, triiodoethylene group, tetraiodoethylene group , chloroethylene group, 1,1-dichloroethylene group, 1,2-dichloroethylene group, trichlorethylene group, tetrachloroethylene group, fluoroethylene group, 1,1-difluoroethylene group, 1,2-difluoroethylene group, trifluoroethylene group, Halogen-containing straight-chain alkylene groups such as tetrafluoroethylene groups; Examples include those replaced with halogen.

Furthermore, when α is a 1,2-phenylene group, -O-α-O- represents a benzenediolate group and -O-α-COO- represents a salicylate group.

L ¹ to L ⁴ in the chemical formula (4) are each independently a halogen atom, an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms; 20, preferably 1 to 10, more preferably 1 to 5 alkoxy groups; having 1 to 20 carbon atoms, preferably 1 to 10, more preferably 1 to 5, halogen atoms, heteroatoms, an alkyl group having at least one of an unsaturated bond or a cyclic structure; or a halogen atom, a heteroatom, It may be an alkoxy group having at least one of an unsaturated bond and a cyclic structure. Here, the halogen atom means a fluorine atom, a chlorine atom, a bromine atom or an iodine atom. A heteroatom means an oxygen atom, a nitrogen atom, or a sulfur atom.

Specifically, L ¹ to L ⁴ are, for example, chain alkyl groups such as methyl group, ethyl group, propyl group, butyl group, isopropyl group, pentyl group, hexyl group, heptyl group, octyl group; cyclopentyl group; , cyclic alkyl groups such as cyclohexyl group; iodomethyl group, bromomethyl group, chloromethyl group, fluoromethyl group, diiodomethyl group, dibromomethyl group, dichloromethyl group, difluoromethyl group, triiodomethyl group, tribromomethyl group, trichloromethyl group, trifluoromethyl group, 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group, 1,2-diiodoethyl group, 1,2-dibromoethyl group, 1,2-dichloroethyl group , 1,2-difluoroethyl group, 2,2-diiodoethyl group, 2,2-dibromoethyl group, 2,2-dichloroethyl group, 2,2-difluoroethyl group, 2,2,2-tribromoethyl group , 2,2,2-trichloroethyl group, 2,2,2-trifluoroethyl group, chain halogen-containing alkyl group such as 1,1,1,3,3,3-hexafluoro-2-propyl group; Cyclic halogen-containing alkyl groups such as 2-iodocyclohexyl group, 2-bromocyclohexyl group, 2-chlorocyclohexyl group, 2-fluorocyclohexyl group; 2-propenyl group, isopropenyl group, 2-butenyl group, 3-butenyl group, etc. Chain alkenyl group; 2-cyclopentenyl group, 2-cyclohexenyl group, cyclic alkenyl group such as 3-cyclohexenyl group; 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1 - Chain alkynyl groups such as pentynyl group, 2-pentynyl group, 3-pentynyl group, 4-pentynyl group; phenyl group, 3-methoxyphenyl group, 4-methoxyphenyl group, 3,5-dimethoxyphenyl group, 4- Aryl groups such as phenoxyphenyl group; 2-iodophenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group, 3- fluorophenyl group, 4-iodophenyl group, 4-bromophenyl group, 4-chlorophenyl group, 4-fluorophenyl group, 3,5-diiodophenyl group, 3,5-dibromophenyl group, 3,5-dichlorophenyl group , Halogen-containing phenyl groups such as 3,5-difluorophenyl groups; Chain alkoxy groups such as methoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy groups; Cyclic groups such as cyclopentoxy and cyclohexoxy groups Alkoxy group; 2-iodoethoxy group, 2-bromoethoxy group, 2-chloroethoxy group, 2-fluoroethoxy group, 1,2-diiodoethoxy group, 1,2-dibromoethoxy group, 1,2-dichlorothoxy group, 1,2-difluoroethoxy group, 2,2-diiodoethoxy group, 2,2-dibromoethoxy group, 2,2-dichloroethoxy group, 2,2-difluoroethoxy group, 2,2,2-tri Chain halogen-containing groups such as bromoethoxy group, 2,2,2-trichloroethoxy group, 2,2,2-trifluoroethoxy group and 1,1,1,3,3,3-hexafluoro-2-propoxy group Alkyl group; cyclic halogen-containing alkyl groups such as 2-iodocyclohexoxy group, 2-bromocyclohexoxy group, 2-chlorocyclohexoxy group, and 2-fluorocyclohexoxy group; 2-propenoxy group, isopropenoxy group, 2-butenoxy group , chain alkenylalkoxy groups such as 3-butenoxy group; cyclic alkenylalkoxy groups such as 2-cyclopentenoxy group, 2-cyclohexenoxy group, and 3-cyclohexenoxy group; 2-propynoxy group, 1-butynoxy group , 2-butynoxy group, 3-butynoxy group, 1-pentynoxy group, 2-pentynoxy group, 3-pentynoxy group, chain alkynylalkoxy groups such as 4-pentynoxy group; phenoxy group, 3-methylphenoxy group, 4-methyl Aryloxy groups such as phenoxy group and 3,5-dimethylphenoxy group; 2-iodophenoxy group, 2-bromophenoxy group, 2-chlorophenoxy group, 2-fluorophenoxy group, 3-iodophenoxy group, 3-bromophenoxy group group, 3-chlorophenoxy group, 3-fluorophenoxy group, 4-iodophenoxy group, 4-bromophenoxy group, 4-chlorophenoxy group, 4-fluorophenoxy group, 3,5-diiodophenoxy group, 3,5 -dibrophenoxy group, 3,5-dichlorophenoxy group, 3,5-difluorophenoxy group and other halogen-containing phenoxy groups.

The L ¹ to L ⁴ are mutually independent and may be the same or different. Moreover, the functional group groups exemplified above are merely examples, and the present invention is not limited to these.

Incidentally, in the chemical formula (4), the n represents a valence. For example, n=1 when M is a monovalent cation, n=2 when it is a divalent cation, and n=3 when it is a trivalent cation.

Specific examples of the boron complex salt represented by the chemical formula (4) include, for example, bisoxalatoborate, bismalonatoborate, bissalicylateborate, bis[1,2'-benzylate(2)-O,O ']borate, oxalatomalonatoborate, oxalatosalicylateborate, oxalato[1,2'-bendiolate(2)-O,O']borate, diiodooxalatoborate, dibromooxalatoborate, dichlorooxalatoborate, Difluorooxalatoborate, iodochlorooxalatoborate, iodobromooxalatoborate, iodofluorooxalatoborate, bromochlorooxalatoborate, bromofluorooxalatoborate, chlorofluorooxalatoborate, diiodomalonatoborate, dibromomalonato Borate, dichloromalonatoborate, difluoromalonatoborate, iodochloromalonatoborate, iodobromomalonatoborate, iodofluoromalonatoborate, bromochloromalonatoborate, bromofluoromalonatoborate, chlorofluoromalonatoborate, diiodine Salicylate borate, dibromosalicylate borate, dichlorosalicylate borate, difluorosalicylate borate, iodochlorosalicylate borate, iodobromo salicylate borate, iodofluorosalicylate borate, bromochlorosalicylate borate , bromofluorosalicylate borate, chlorofluorosalicylate borate, diiodo[1,2′-bendiolate(2)-O,O′]borate, dibromo[1,2′-bendiolate(2)-O,O′ ] borate, dichloro [1,2'-bendiolate (2) -O, O'] borate, difluoro [1,2'-bendiolate (2) -O, O'] borate, iodochloro [1,2'-bendiolate ( 2) -O,O']borate, iodobromo[1,2'-bendiolate(2)-O,O']borate, iodofluoro[1,2'-bendiolate(2)-O,O']borate, bromochloro [1,2'-bendiolate (2)-O,O']borate, bromofluoro[1,2'-bendiolate (2)-O,O']borate, chlorofluoro[1,2'-bendiolate (2) —O,O′]borate, tetraiodoborate, tetrabromoborate, tetrachloroborate, tetrafluoroborate, iodotribromoborate, iodotrichloroborate, iodotrifluoroborate, diiododibromoborate, diiododichloroborate, diiodine difluoroborate, triiodobromoborate, triiodochloroborate, triiodofluoroborate, bromotrichloroborate, bromotrifluoroborate, dibromodichloroborate, dibromodifluoroborate, tribromochloroborate, tribromofluoroborate, chlorotrifluoroborate, Dichlorodifluoroborate, iodobromochlorofluoroborate, tetramethylborate, tetraethylborate, tetraphenylborate, tetramethoxyborate, tetraethoxyborate, tetraphenoxyborate, ethyldimethylphenylborate, butylethylmethylphenylborate, ethoxydimethoxyphenoxyborate, dimethyl oxalatoborate, dimethylmalonatoborate, dimethylsalicylateborate, dimethyl[1,2'-bendiolate(2)-O,O']borate, ethylmethyloxalatoborate, phenylmethyloxalatoborate, iodomethyloxalato Borate, bromomethyloxalatoborate, chloromethyloxalatoborate, fluoromethyloxalatoborate, iodoethyloxalatoborate, bromoethyloxalatoborate, chloroethyloxalatoborate, fluoroethyloxalatoborate, ethoxymethoxyoxalatoborate, Those with boron complex anions such as iodomethoxyoxalatoborate, bromomethoxyoxalatoborate, chloromethoxyoxalatoborate or fluoromethoxyoxalatoborate are included.

Among the exemplified boron complex salts, boron complex anions of bisoxalatoborate, bissalicylateborate or bis[1,2'-bendiolate(2)-O,O']borate are preferred from the viewpoint of availability. Boron complex salts with are preferred.

In addition, the specific examples of the boron complex salt represented by the chemical formula (4) shown above are merely examples, and the present embodiment is not limited to these.

2. Phosphorus Complex Salt The phosphorus complex salt is specifically represented by the following chemical formula (5).

Mn ⁺ and the valence n in the chemical formula (5) are the same as described in the chemical formula (4). Therefore, detailed description thereof will be omitted.

L ⁵ to L ¹⁰ in the chemical formula (5) are each independent, and at least one arbitrarily selected combination is -OOC-COO-, -OOC-O-, -OOC-β-COO- , -O-β-O- or -OOC-β-O- which forms a ring structure. In that case, β is a hydrocarbon group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms; or 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 5 and represents a hydrocarbon group having a heteroatom, an unsaturated bond or a cyclic structure. When the L ⁵ to L ¹⁰ have two or more pairs of any one of the -OOC-β-COO-, -O-β-O- and -OOC-β-O- ring structures, each β is can be different. Here, a heteroatom means an oxygen atom, a nitrogen atom or a sulfur atom.

The β is not particularly limited, and examples thereof include linear alkylene groups such as a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, and a nonylene group; methylene group, bromomethylene group, dibromomethylene group, fluoromethylene group, difluoromethylene group, iodoethylene group, 1,1-diiodoethylene group, 1,2-diiodoethylene group, triiodoethylene group, tetraiodoethylene group , chloroethylene group, 1,1-dichloroethylene group, 1,2-dichloroethylene group, trichlorethylene group, tetrachloroethylene group, fluoroethylene group, 1,1-difluoroethylene group, 1,2-difluoroethylene group, trifluoroethylene group, Halogen-containing straight-chain alkylene groups such as tetrafluoroethylene groups; Examples include those replaced with halogen.

Furthermore, when β is a 1,2-phenylene group, —O-β-O— represents a benzenediolate group, and —O-β-COO— represents a salicylate group.

In addition, L ⁵ to L ¹⁰ in the chemical formula (5) each independently represent at least one of a halogen atom; an alkyl group; an alkoxy group; an alkylthio group; a halogen atom, a hetero atom, or an unsaturated bond. (hereinafter referred to as "an alkyl group having a halogen atom etc."); an alkoxy group having at least one of a halogen atom, hetero atom or unsaturated bond (hereinafter referred to as an "alkoxy group having a halogen atom etc." or an alkylthio group having at least one of a halogen atom, a heteroatom, or an unsaturated bond (hereinafter referred to as "an alkylthio group having a halogen atom, etc."). The alkyl group, alkoxy group, alkylthio group, alkyl group having a halogen atom or the like, alkoxy group having a halogen atom or the like, and alkylthio group having a halogen atom or the like have a carbon number in the range of 1 to 20, preferably 1 to 10. , more preferably 1-4. The number of unsaturated bonds is preferably in the range of 1-10, more preferably in the range of 1-5, and particularly preferably in the range of 1-3.

The halogen atom and heteroatom are the same as those described in the chemical formula (4). In the alkyl group having a halogen atom, etc., the alkoxy group having a halogen atom, etc., and the alkylthio group having a halogen atom, etc., the halogen atom and heteroatom are part or all of hydrogen in these functional groups. may be substituted with any of these halogen atoms and/or heteroatoms.

Specifically, L ⁵ to L ¹⁰ are, for example, chain alkyl groups such as methyl group, ethyl group, propyl group, butyl group, isopropyl group, pentyl group, hexyl group, heptyl group, octyl group; cyclopentyl group; , cyclic alkyl groups such as cyclohexyl group; iodomethyl group, bromomethyl group, chloromethyl group, fluoromethyl group, diiodomethyl group, dibromomethyl group, dichloromethyl group, difluoromethyl group, triiodomethyl group, tribromomethyl group, trichloromethyl group, trifluoromethyl group, 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group, 1,2-diiodoethyl group, 1,2-dibromoethyl group, 1,2-dichloroethyl group , 1,2-difluoroethyl group, 2,2-diiodoethyl group, 2,2-dibromoethyl group, 2,2-dichloroethyl group, 2,2-difluoroethyl group, 2,2,2-tribromoethyl group , 2,2,2-trichloroethyl group, 2,2,2-trifluoroethyl group, chain halogen-containing alkyl group such as hexafluoro-2-propyl group; 2-iodocyclohexyl group, 2-bromocyclohexyl group, Cyclic halogen-containing alkyl groups such as 2-chlorocyclohexyl group and 2-fluorocyclohexyl group; chain alkenyl groups such as 2-propenyl group, isopropenyl group, 2-butenyl group and 3-butenyl group; 2-cyclopentenyl group, Cyclic alkenyl groups such as 2-cyclohexenyl group and 3-cyclohexenyl group; 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3-pentynyl chain alkynyl groups such as groups and 4-pentynyl groups; aryl groups such as phenyl groups, 3-methoxyphenyl groups, 4-methoxyphenyl groups, 3,5-dimethoxyphenyl groups and 4-phenoxyphenyl groups; group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group, 3-fluorophenyl group, 4-iodophenyl group, 4- Halogen-containing groups such as bromophenyl, 4-chlorophenyl, 4-fluorophenyl, 3,5-diiodophenyl, 3,5-dibromophenyl, 3,5-dichlorophenyl and 3,5-difluorophenyl groups Phenyl group; methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, chain alkoxy group such as hexoxy group; cyclopentoxy group, cyclic alkoxy group such as cyclohexoxy group; 2-iodoethoxy group, 2-bromo ethoxy group, 2-chloroethoxy group, 2-fluoroethoxy group, 1,2-diiodoethoxy group, 1,2-dibromoethoxy group, 1,2-dichloroethoxy group, 1,2-difluoroethoxy group, 2, 2-diiodoethoxy group, 2,2-dibromoethoxy group, 2,2-dichloroethoxy group, 2,2-difluoroethoxy group, 2,2,2-tribromoethoxy group, 2,2,2-trichloroethoxy group chain halogen-containing alkoxy groups such as groups, 2,2,2-trifluoroethoxy groups and hexafluoro-2-propoxy groups; 2-iodocyclohexoxy groups, 2-bromocyclohexoxy groups, 2-chlorocyclohexoxy groups, Cyclic halogen-containing alkoxy groups such as 2-fluorocyclohexoxy group; chain alkenylalkoxy groups such as 2-propenoxy group, isopropenoxy group, 2-butenoxy group, and 3-butenoxy group; 2-cyclopentenoxy group, 2-cyclohexy cyclic alkenylalkoxy groups such as senoxy group and 3-cyclohexenoxy group; phenoxy group, 3-methylphenoxy group, 4-methylphenoxy group, aryloxy group such as 3,5-dimethylphenoxy group; 2-iodophenoxy group, 2- Bromophenoxy group, 2-chlorophenoxy group, 2-fluorophenoxy group, 3-iodophenoxy group, 3-bromophenoxy group, 3-chlorophenoxy group, 3-fluorophenoxy group, 4-iodophenoxy group, 4-bromophenoxy group, 4-chlorophenoxy group, 4-fluorophenoxy group, 3,5-diiodophenoxy group, 3,5-dibrophenoxy group, 3,5-dichlorophenoxy group, 3,5-difluorophenoxy group, etc. Halogenphenoxy group; methylthio group, ethylthio group, propylthio group, butylthio group, iopropylthio group, pentylthio group, alkylthio group such as hexylthio group, and the like.

Examples of the phosphorus compound represented by the chemical formula (5) include easily available lithium difluorobisoxalate phosphate, sodium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, sodium tetrafluorobisoxalate phosphate, and the like. are mentioned.

3. Lewis Acid Complex Salt The Lewis acid complex anion in the Lewis acid complex salt consists of an inorganic anion or an organic anion and a Lewis acid such as BF ₃ , PF ₅ and AlF ₃ .

The inorganic anion is not particularly limited, and examples thereof include carbonate anion, sulfate anion, fluorosulfate anion, chlorosulfate anion, bromosulfate anion, iodosulfate anion, phosphate anion, monofluorophosphate anion, monomonophosphate anion, and monobromoline. acid anions, monoiophosphate anions, difluorophosphate anions, dichlorophosphate anions, dibromophosphate anions, diiophosphate anions, and the like.

The organic anions are not particularly limited, and examples thereof include organic carboxylate anions, organic sulfonate anions, and organic phosphate anions. Furthermore, the organic carboxylate anion is not particularly limited, and examples include formate anion, acetate anion, propionate anion, butyrate anion, valerate anion, trifluoroacetate anion, pentafluoropropionate anion, heptafluorobutyrate anion, nonafluorobutyrate anion, herbal acid anion and the like. The organic sulfonate anion is not particularly limited, and examples thereof include methanesulfonate anion, ethanesulfonate anion, propanesulfonate, butanesulfonate anion, trifluoromethanesulfonate anion, pentafluoroethanesulfonate anion, and heptafluoropropane. Examples include sulfonate anions, nonafluorobutanesulfonate anions, and the like. The organic phosphate anion is not particularly limited, and examples thereof include octyl phosphate anion, dodecyl phosphate anion, octadecyl phosphate anion, phenyl phosphate anion, nonylphenyl phosphate anion, and the like.

The Lewis acid that forms the Lewis acid complex salt is not particularly limited, and examples thereof include those represented by the following chemical formulas (6) to (8).

In the chemical formula (6), A ¹ to A ³ each independently represent at least one of a hydrogen atom; a halogen atom; an alkyl group, an alkoxy group, an alkylthio group; a halogen atom, a hetero atom, or an unsaturated bond; (hereinafter referred to as "an alkyl group having a halogen atom etc."); an alkoxy group having at least one of a halogen atom, a hetero atom or an unsaturated bond (hereinafter referred to as an "alkoxy group having a halogen atom etc. ); or an alkylthio group having at least one of a halogen atom, a heteroatom, or an unsaturated bond (hereinafter referred to as "an alkylthio group having a halogen atom, etc."). The alkyl group, alkoxy group, alkylthio group, alkyl group having a halogen atom or the like, alkoxy group having a halogen atom or the like, and alkylthio group having a halogen atom or the like have a carbon number in the range of 1 to 20, preferably 1 to 10. , more preferably 1-4. The number of unsaturated bonds is preferably in the range of 1-10, more preferably in the range of 1-5, and particularly preferably in the range of 1-3.

More specifically, A ¹ to A ³ are, for example, chain alkyl groups such as methyl group, ethyl group, propyl group, butyl group, isopropyl group, pentyl group, hexyl group, heptyl group and octyl group; cyclopentyl cyclic alkyl groups such as cyclohexyl group; iodomethyl group, bromomethyl group, chloromethyl group, fluoromethyl group, diiodomethyl group, dibromomethyl group, dichloromethyl group, difluoromethyl group, triiodomethyl group, tribromomethyl group, trichloro methyl group, trifluoromethyl group, 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group, 1,2-diiodoethyl group, 1,2-dibromoethyl group, 1,2-dichloroethyl group, 1,2-difluoroethyl group, 2,2-diiodoethyl group, 2,2-dibromoethyl group, 2,2-dichloroethyl group, 2,2-difluoroethyl group, 2,2,2-tribromoethyl 2,2,2-trichloroethyl group, 2,2,2-trifluoroethyl group, chain halogen-containing alkyl group such as hexafluoro-2-propyl group; 2-iodocyclohexyl group, 2-bromocyclohexyl group , 2-chlorocyclohexyl group, cyclic halogen-containing alkyl group such as 2-fluorocyclohexyl group; 2-propenyl group, isopropenyl group, 2-butenyl group, chain alkenyl group such as 3-butenyl group; 2-cyclopentenyl group , 2-cyclohexenyl group, cyclic alkenyl groups such as 3-cyclohexenyl group; 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3- chain alkynyl groups such as pentynyl group and 4-pentynyl group; aryl groups such as phenyl group, 3-methoxyphenyl group, 4-methoxyphenyl group, 3,5-dimethoxyphenyl group and 4-phenoxyphenyl group; 2-iodine phenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group, 3-fluorophenyl group, 4-iodophenyl group, 4 -bromophenyl group, 4-chlorophenyl group, 4-fluorophenyl group, 3,5-diiodophenyl group, 3,5-dibromophenyl group, 3,5-dichlorophenyl group, 3,5-difluorophenyl group, etc. Halogen phenyl group; methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, chain alkoxy group such as hexoxy group; cyclopentoxy group, cyclic alkoxy group such as cyclohexoxy group; 2-iodoethoxy group, 2- bromoethoxy group, 2-chloroethoxy group, 2-fluoroethoxy group, 1,2-diiodoethoxy group, 1,2-dibromoethoxy group, 1,2-dichloroethoxy group, 1,2-difluoroethoxy group, 2 ,2-diiodoethoxy group, 2,2-dibromoethoxy group, 2,2-dichloroethoxy group, 2,2-difluoroethoxy group, 2,2,2-tribromoethoxy group, 2,2,2-trichloro Chain halogen-containing alkoxy groups such as ethoxy group, 2,2,2-trifluoroethoxy group, hexafluoro-2-propoxy group; 2-iodocyclohexoxy group, 2-bromocyclohexoxy group, 2-chlorocyclohexoxy group , cyclic halogen-containing alkoxy groups such as 2-fluorocyclohexoxy group; 2-propenoxy group, isopropenoxy group, 2-butenoxy group, chain alkenylalkoxy groups such as 3-butenoxy group; 2-cyclopentenoxy group, 2- cyclic alkenylalkoxy groups such as cyclohexenoxy group and 3-cyclohexenoxy group; chain alkynylalkoxy groups such as pentynoxy group and 4-pentynoxy group; aryloxy groups such as phenoxy group, 3-methylphenoxy group, 4-methylphenoxy group and 3,5-dimethylphenoxy group; 2-iodophenoxy group, 2 -bromophenoxy group, 2-chlorophenoxy group, 2-fluorophenoxy group, 3-iodophenoxy group, 3-bromophenoxy group, 3-chlorophenoxy group, 3-fluorophenoxy group, 4-iodophenoxy group, 4-bromo phenoxy group, 4-chlorophenoxy group, 4-fluorophenoxy group, 3,5-diiodophenoxy group, 3,5-dibrophenoxy group, 3,5-dichlorophenoxy group, 3,5-difluorophenoxy group, etc. Halogen-containing phenoxy groups; alkylthio groups such as methylthio, ethylthio, propylthio, butylthio, iopropylthio, pentylthio and hexylthio groups.

In the chemical formula (7), each of A ⁴ to A ⁸ is independently at least one of a hydrogen atom; a halogen atom; an alkyl group; an alkoxy group; an alkylthio group; (hereinafter referred to as "an alkyl group having a halogen atom, etc."); an alkoxy group having at least one of a halogen atom, a hetero atom, or an unsaturated bond (hereinafter referred to as an "alkoxy or an alkylthio group having at least one of a halogen atom, a heteroatom, or an unsaturated bond (hereinafter referred to as an "alkylthio group having a halogen atom, etc."). The alkyl group, alkoxy group, alkylthio group, alkyl group having a halogen atom or the like, alkoxy group having a halogen atom or the like, and alkylthio group having a halogen atom or the like have a carbon number in the range of 1 to 20, preferably 1 to 10. , more preferably 1-4. The number of unsaturated bonds is preferably in the range of 1-10, more preferably in the range of 1-5, and particularly preferably in the range of 1-3.

A ⁴ to A ⁸ are not limited, and specific examples include chain alkyl groups such as methyl group, ethyl group, propyl group, butyl group, isopropyl group, pentyl group, hexyl group, heptyl group and octyl group. Cyclic alkyl groups such as cyclopentyl group and cyclohexyl group; iodomethyl group, bromomethyl group, chloromethyl group, fluoromethyl group, diiodomethyl group, dibromomethyl group, dichloromethyl group, difluoromethyl group, triiodomethyl group, tribromomethyl group , trichloromethyl group, trifluoromethyl group, 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group, 1,2-diiodoethyl group, 1,2-dibromoethyl group, 1,2- dichloroethyl group, 1,2-difluoroethyl group, 2,2-diiodoethyl group, 2,2-dibromoethyl group, 2,2-dichloroethyl group, 2,2-difluoroethyl group, 2,2,2-tri Chain halogen-containing alkyl groups such as bromoethyl group, 2,2,2-trichloroethyl group, 2,2,2-trifluoroethyl group, hexafluoro-2-propyl group; 2-iodocyclohexyl group, 2-bromo Cyclic halogen-containing alkyl groups such as cyclohexyl group, 2-chlorocyclohexyl group and 2-fluorocyclohexyl group; chain alkenyl groups such as 2-propenyl group, isopropenyl group, 2-butenyl group and 3-butenyl group; 2-cyclo Pentenyl group, 2-cyclohexenyl group, cyclic alkenyl groups such as 3-cyclohexenyl group; 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl group, 2-pentynyl group, chain alkynyl groups such as 3-pentynyl group and 4-pentynyl group; aryl groups such as phenyl group, 3-methoxyphenyl group, 4-methoxyphenyl group, 3,5-dimethoxyphenyl group and 4-phenoxyphenyl group;2 -iodophenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group, 3-fluorophenyl group, 4-iodophenyl group , 4-bromophenyl group, 4-chlorophenyl group, 4-fluorophenyl group, 3,5-diiodophenyl group, 3,5-dibromophenyl group, 3,5-dichlorophenyl group, 3,5-difluorophenyl group, etc. Halogen-containing phenyl group; methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, chain alkoxy group such as hexoxy group; cyclopentoxy group, cyclic alkoxy group such as cyclohexoxy group; 2-iodoethoxy group, 2-bromoethoxy group, 2-chloroethoxy group, 2-fluoroethoxy group, 1,2-diiodoethoxy group, 1,2-dibromoethoxy group, 1,2-dichloroethoxy group, 1,2-difluoroethoxy group , 2,2-diiodoethoxy group, 2,2-dibromoethoxy group, 2,2-dichloroethoxy group, 2,2-difluoroethoxy group, 2,2,2-tribromoethoxy group, 2,2,2 - Chain halogen-containing alkoxy groups such as trichloroethoxy group, 2,2,2-trifluoroethoxy group, hexafluoro-2-propoxy group; 2-iodocyclohexoxy group, 2-bromocyclohexoxy group, 2-chlorocyclohexy Cyclic halogen-containing alkoxy groups such as soxy group and 2-fluorocyclohexoxy group; chain alkenylalkoxy groups such as 2-propenoxy group, isopropenoxy group, 2-butenoxy group and 3-butenoxy group; 2-cyclopentenoxy group, Cyclic alkenylalkoxy groups such as 2-cyclohexenoxy group and 3-cyclohexenoxy group; chain alkynylalkoxy groups such as 3-pentynoxy group and 4-pentynoxy group; aryloxy groups such as phenoxy group, 3-methylphenoxy group, 4-methylphenoxy group and 3,5-dimethylphenoxy group; 2-iodophenoxy group , 2-bromophenoxy group, 2-chlorophenoxy group, 2-fluorophenoxy group, 3-iodophenoxy group, 3-bromophenoxy group, 3-chlorophenoxy group, 3-fluorophenoxy group, 4-iodophenoxy group, 4 -bromophenoxy group, 4-chlorophenoxy group, 4-fluorophenoxy group, 3,5-diiodophenoxy group, 3,5-dibrophenoxy group, 3,5-dichlorophenoxy group, 3,5-difluorophenoxy group halogen-containing phenoxy groups such as; alkylthio groups such as methylthio, ethylthio, propylthio, butylthio, iopropylthio, pentylthio and hexylthio.

In the chemical formula (8), A ⁹ to A ¹¹ each independently represent at least one of a hydrogen atom; a halogen atom; an alkyl group; an alkoxy group; an alkylthio group; (hereinafter referred to as "an alkyl group having a halogen atom, etc."); an alkoxy group having at least one of a halogen atom, a hetero atom, or an unsaturated bond (hereinafter referred to as an "alkoxy or an alkylthio group having at least one of a halogen atom, a heteroatom, or an unsaturated bond (hereinafter referred to as an "alkylthio group having a halogen atom, etc."). The alkyl group, alkoxy group, alkylthio group, alkyl group having a halogen atom or the like, alkoxy group having a halogen atom or the like, and alkylthio group having a halogen atom or the like have a carbon number in the range of 1 to 20, preferably 1 to 10. , more preferably 1-4. The number of unsaturated bonds is preferably in the range of 1-10, more preferably in the range of 1-5, and particularly preferably in the range of 1-3.

A ⁹ to A ¹¹ are not limited, and specific examples include chain alkyl groups such as methyl group, ethyl group, propyl group, butyl group, isopropyl group, pentyl group, hexyl group, heptyl group and octyl group. Cyclic alkyl groups such as cyclopentyl group and cyclohexyl group; iodomethyl group, bromomethyl group, chloromethyl group, fluoromethyl group, diiodomethyl group, dibromomethyl group, dichloromethyl group, difluoromethyl group, triiodomethyl group, tribromomethyl group , trichloromethyl group, trifluoromethyl group, 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group, 1,2-diiodoethyl group, 1,2-dibromoethyl group, 1,2- dichloroethyl group, 1,2-difluoroethyl group, 2,2-diiodoethyl group, 2,2-dibromoethyl group, 2,2-dichloroethyl group, 2,2-difluoroethyl group, 2,2,2-tri Chain halogen-containing alkyl groups such as bromoethyl group, 2,2,2-trichloroethyl group, 2,2,2-trifluoroethyl group, hexafluoro-2-propyl group; 2-iodocyclohexyl group, 2-bromo Cyclic halogen-containing alkyl groups such as cyclohexyl group, 2-chlorocyclohexyl group and 2-fluorocyclohexyl group; chain alkenyl groups such as 2-propenyl group, isopropenyl group, 2-butenyl group and 3-butenyl group; 2-cyclo Pentenyl group, 2-cyclohexenyl group, cyclic alkenyl groups such as 3-cyclohexenyl group; 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl group, 2-pentynyl group, chain alkynyl groups such as 3-pentynyl group and 4-pentynyl group; aryl groups such as phenyl group, 3-methoxyphenyl group, 4-methoxyphenyl group, 3,5-dimethoxyphenyl group and 4-phenoxyphenyl group;2 -iodophenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group, 3-fluorophenyl group, 4-iodophenyl group , 4-bromophenyl group, 4-chlorophenyl group, 4-fluorophenyl group, 3,5-diiodophenyl group, 3,5-dibromophenyl group, 3,5-dichlorophenyl group, 3,5-difluorophenyl group, etc. Halogen-containing phenyl group; methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, chain alkoxy group such as hexoxy group; cyclopentoxy group, cyclic alkoxy group such as cyclohexoxy group; 2-iodoethoxy group, 2-bromoethoxy group, 2-chloroethoxy group, 2-fluoroethoxy group, 1,2-diiodoethoxy group, 1,2-dibromoethoxy group, 1,2-dichloroethoxy group, 1,2-difluoroethoxy group , 2,2-diiodoethoxy group, 2,2-dibromoethoxy group, 2,2-dichloroethoxy group, 2,2-difluoroethoxy group, 2,2,2-tribromoethoxy group, 2,2,2 - Chain halogen-containing alkoxy groups such as trichloroethoxy group, 2,2,2-trifluoroethoxy group, hexafluoro-2-propoxy group; 2-iodocyclohexoxy group, 2-bromocyclohexoxy group, 2-chlorocyclohexy Cyclic halogen-containing alkoxy groups such as soxy group and 2-fluorocyclohexoxy group; chain alkenylalkoxy groups such as 2-propenoxy group, isopropenoxy group, 2-butenoxy group and 3-butenoxy group; 2-cyclopentenoxy group, Cyclic alkenylalkoxy groups such as 2-cyclohexenoxy group and 3-cyclohexenoxy group; chain alkynylalkoxy groups such as 3-pentynoxy group and 4-pentynoxy group; aryloxy groups such as phenoxy group, 3-methylphenoxy group, 4-methylphenoxy group and 3,5-dimethylphenoxy group; 2-iodophenoxy group , 2-bromophenoxy group, 2-chlorophenoxy group, 2-fluorophenoxy group, 3-iodophenoxy group, 3-bromophenoxy group, 3-chlorophenoxy group, 3-fluorophenoxy group, 4-iodophenoxy group, 4 -bromophenoxy group, 4-chlorophenoxy group, 4-fluorophenoxy group, 3,5-diiodophenoxy group, 3,5-dibrophenoxy group, 3,5-dichlorophenoxy group, 3,5-difluorophenoxy group halogen-containing phenoxy groups such as; alkylthio groups such as methylthio, ethylthio, propylthio, butylthio, iopropylthio, pentylthio and hexylthio.

Specific examples of Lewis acids represented by chemical formulas (6) to (8) include BF ₃ , PF ₅ , AlF _{3 and} AlCl ₃ . In addition, among the Lewis acids represented by the chemical formulas (6) to (8), those containing a halogen element in the chemical structure are preferable from the viewpoint of further enhancing the Lewis acidity. Specific examples of such Lewis acids include BF ₃ , PF ₅ , AlCl ₃ and the like.

The cation in the Lewis acid complex salt is, like the boron complex salt, any one selected from the group consisting of alkali metal ions, alkaline earth metal ions, aluminum ions, transition metal ions and onium ions. be. Therefore, detailed description thereof will be omitted.

4. Phosphate Ester Salt The phosphate ester salt is specifically represented by the following chemical formula (9).

Mn ⁺ and the valence n in the chemical formula (9) are the same as described in the chemical formula (4). Therefore, detailed description thereof will be omitted.

In the chemical formula (9), R ¹ and R ² are each independently a hydrocarbon group having 1 to 20 carbon atoms; or a hydrocarbon group having at least one of unsaturated bonds. Alternatively, R ¹ and R ² are a hydrocarbon group having 1 to 20 carbon atoms or a range of 1 to 20 carbon atoms and have at least one of a halogen atom, a hetero atom and an unsaturated bond. Represents any hydrocarbon group that bonds to each other to form a cyclic structure.

Specific examples of the hydrocarbon group or the hydrocarbon group having a halogen atom or the like include, for example, a methyl group, an ethyl group, a propyl group, a butyl group, an isopropyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, and the like. Cyclic alkyl group such as cyclopentyl group and cyclohexyl group; 2-iodoethyl group, 2-bromoethyl group, 2-chloroethyl group, 2-fluoroethyl group, 1,2-diiodoethyl group, 1,2-dibromo ethyl group, 1,2-dichloroethyl group, 1,2-difluoroethyl group, 2,2-diiodoethyl group, 2,2-dibromoethyl group, 2,2-dichloroethyl group, 2,2-difluoroethyl group, Chain halogen-containing alkyl groups such as 2,2,2-tribromoethyl group, 2,2,2-trichloroethyl group, 2,2,2-trifluoroethyl group, hexafluoro-2-propyl group; Cyclic halogen-containing alkyl groups such as iodocyclohexyl group, 2-bromocyclohexyl group, 2-chlorocyclohexyl group and 2-fluorocyclohexyl group; chains such as 2-propenyl group, isopropenyl group, 2-butenyl group and 3-butenyl group Cyclic alkenyl group; 2-cyclopentenyl group, 2-cyclohexenyl group, cyclic alkenyl group such as 3-cyclohexenyl group; 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl phenyl group, 3-methoxyphenyl group, 4-methoxyphenyl group, 3,5-dimethoxyphenyl group, 4-phenoxyphenyl Aryl groups such as groups; 2-iodophenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, 3-iodophenyl group, 3-bromophenyl group, 3-chlorophenyl group, 3-fluorophenyl group, 4-iodophenyl group, 4-bromophenyl group, 4-chlorophenyl group, 4-fluorophenyl group, 3,5-diiodophenyl group, 3,5-dibromophenyl group, 3,5-dichlorophenyl group, 3 halogen-containing phenyl groups such as ,5-difluorophenyl group; naphthyl groups such as 1-naphthyl group, 2-naphthyl group and 3-amino-2-naphthyl group;

The halogen atom means a fluorine, chlorine, bromine or iodine atom, and some or all of the hydrogen atoms in the hydrocarbon group may be substituted with any of these halogen atoms. In addition, heteroatom means an atom such as oxygen, nitrogen or sulfur. Furthermore, the number of unsaturated bonds is preferably in the range of 1-10, more preferably in the range of 1-5, and particularly preferably in the range of 1-3.

Furthermore, R ¹ and R ² may be either the hydrocarbon group or the hydrocarbon group having a halogen atom or the like, and may be bonded to each other to form a cyclic structure. In this case, the hydrocarbon group or the hydrocarbon group having a halogen atom or the like specifically includes, for example, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, straight-chain alkylene groups such as nonylene groups; -diiodoethylene group, triiodoethylene group, tetraiodoethylene group, chloroethylene group, 1,1-dichloroethylene group, 1,2-dichloroethylene group, trichlorethylene group, tetrachloroethylene group, fluoroethylene group, 1,1-difluoroethylene Halogen-containing linear alkylene groups such as groups, 1,2-difluoroethylene groups, trifluoroethylene groups, and tetrafluoroethylene groups; and cyclic hydrocarbon groups such as and those partially or entirely replaced with halogen atoms.

R ¹ and R ² may be the same or different in the functional group group exemplified above. Moreover, the functional group groups exemplified above are merely examples, and the present invention is not limited to these.

Specific examples of the anion in the phosphate ester salt represented by the chemical formula (9) include dimethyl phosphate anion, diethyl phosphate anion, dipropyl phosphate anion, bis(2,2,2-trifluoroethyl)phosphorus acid anion, bis(1,1,1,3,3,3-hexafluoroisopropyl)phosphate anion, and the like.

In other electrolytes such as boron complex salts exemplified above, BF ₄ ⁻ , PF ₆ ⁻ , N(CF ₃ SO ₂ ) ₂ ⁻ , or N(SO ₂ F ) ₂ ^- cations are preferred, and those with BF ₄ ^- , PF ₆ ^- or N(SO ₂ F) ₂ ^- cations are more preferred. Moreover, from the viewpoint of improving battery characteristics, those having PF ₆ ^— or N(SO ₂ F) ₂ ^— cations are preferable.

<Additive>
The non-aqueous electrolytic solution of the present embodiment may contain additives in addition to the non-aqueous solvent and the electrolyte.
Additives are not particularly limited, and examples include boric acid esters, acid anhydrides, cyclic carbonates having unsaturated bonds, cyclic carbonates having halogen atoms, cyclic sulfonic acid esters, amines having an acetoacetyl group, and phosphorus compounds. at least one compound selected from the group consisting of

1. Boric acid ester As the boric acid ester, there are no particular restrictions on the type of the boric acid ester as long as it does not impair the characteristics of the non-aqueous electrolytic solution of the present embodiment and the secondary battery using the same, and various ones can be selected. be able to. Specifically, for example, trimethyl borate, triethyl borate, triisopropyl borate, tributyl borate, tripentyl borate, trihexyl borate, triheptyl borate, triphenyl borate, tris(2, 2,2-iodoethyl), tris(2,2,2-tribromoethyl)borate, tris(2,2,2-trichloroethyl)borate, tris(2,2,2-trifluoroethyl)borate tris(4-iodophenyl) acid, tris(4-bromophenyl) borate, tris(4-chlorophenyl) borate, tris(4-fluorophenyl) borate, diethylmethyl borate, ethyldimethyl borate and the like. be done.

2. Acid anhydride As the acid anhydride, there are no particular restrictions on the type thereof, and various ones can be selected as long as they do not impair the characteristics of the non-aqueous electrolyte of the present embodiment and the secondary battery using the same. be able to. Specifically, for example, acetic anhydride, propionic anhydride, butyric anhydride, valeric anhydride, hexanoic anhydride, heptanoic anhydride, octanoic anhydride, nonanoic anhydride, decanoic anhydride , eicosanoic anhydride, docosanoic anhydride, benzoic anhydride, 4-methoxybenzoic anhydride, diphenylacetic anhydride, crotonic anhydride, cyclohexanecarboxylic anhydride, elaidic anhydride, isobutyric anhydride, isovaleric anhydride, lauric anhydride, linoleic anhydride, myristic anhydride, angelic anhydride, chlorodifluoroacetic anhydride, trichloroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, 4- Linear carboxylic anhydrides such as trifluoromethylbenzoic anhydride, phthalic anhydride, 3-acetamidophthalic anhydride, 4,4′-carbonyldiphthalic anhydride, 4,4′-biphthalic anhydride , 3-iodophthalic anhydride, 3-bromophthalic anhydride, 3-chlorophthalic anhydride, 3-fluorophthalic anhydride, 4-iodophthalic anhydride, 4-bromophthalic anhydride, 4-chlorophthalic anhydride , 4-fluorophthalic anhydride, 4,5-diiodophthalic anhydride, 4,5-dibromophthalic anhydride, 4,5-dichlorophthalic anhydride, 4,5-difluorophthalic anhydride, 4, 4′-sulfonyldiphthalic anhydride, 3-nitrophthalic anhydride, 4-nitrophthalic anhydride, exo-3,6-epoxyhexahydrophthalic anhydride, exo-3,6-epoxy-1,2, 3,6-tetrahydrophthalic anhydride, tetraiodophthalic anhydride, tetrachlorophthalic anhydride, tetrafluorophthalic anhydride, 4-tert-butylphthalic anhydride, 4-ethynylphthalic anhydride, 4, 4'-(Hexafluoroisopropylidene)diphthalic anhydride, succinic anhydride, (R)-(+)-2-acetoxysuccinic anhydride, (S)-(-)-2-acetoxysuccinic anhydride , 2-butene-1-ylsuccinic anhydride, butylsuccinic anhydride, decylsuccinic anhydride, 2,3-dimethylsuccinic anhydride, 2-dodecen-1-ylsuccinic anhydride, dodecylsuccinic anhydride, octa Decenicosuccinic anhydride, (2,7-octadien-1-yl)succinic anhydride, n-octylsuccinic anhydride, hexadecylsuccinic anhydride, maleic anhydride, 2,3-bis(2 ,4,5-trimethyl-3-thienyl)maleic anhydride, 2-(-2-carboxyethyl)-3-methyl-maleic anhydride, 2,3-dimethylmaleic anhydride, 2,3-diphenyl maleic anhydride, phenylmaleic anhydride, 4-pentene-1,2-dicarboxylic anhydride, 2,3-anthracenedicarboxylic anhydride, bicyclo[2,2,2]oct-5-ene-2, 3-dicarboxylic anhydride, 4-bromo-1,8-naphthalenedicarboxylic anhydride, (±)-trans-1,2-cyclohexanedicarboxylic anhydride, cis-4-cyclohexene-1,2-dicarboxylic anhydride 2,5-dibromo-3,4-thiophenedicarboxylic anhydride, 5,6-dihydro-1,4-dithiin-2,3-dicarboxylic anhydride, 2,2′-biphenyldicarboxylic anhydride, 4-methylcyclohexane-1,2-dicarboxylic anhydride, 3-methyl-4-cyclohexene-1,2-dicarboxylic anhydride, 4-methyl-4-cyclohexene-1,2-dicarboxylic anhydride, 2, 3-naphthalenedicarboxylic anhydride, 3,4-thiophenedicarboxylic anhydride, 1,8-naphthalenedicarboxylic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, 1,2-cyclopropanedicarboxylic anhydride glutaric anhydride, 3,3-pentamethyleneglutaric anhydride, 2,2-dimethylglutaric anhydride, 3,3-dimethylglutaric anhydride, 3-methylglutaric anhydride, 2-phthalimidoglutaric Acid anhydride, 3,3-tetramethyleneglutaric anhydride, N-methylisatoic anhydride, 4-iodoisatoic anhydride, 4-bromoisatoic anhydride, 4-chloroisatoic anhydride, 4-fluoroisatoic anhydride , 5-iodoisatoic anhydride, 5-bromoisatoic anhydride, 5-chloroisatoic anhydride, 5-fluoroisatoic anhydride, itaconic anhydride, caronic anhydride, citraconic anhydride, diglycolic anhydride , 1,2-naphthalic anhydride, pyromellitic anhydride, het acid anhydride, cyclic carboxylic anhydrides such as 2,2,3,3,4,4-hexafluoropentanedianhydride, trifluoromethane Sulfonic anhydride, linear sulfonic anhydride such as p-toluenesulfonic anhydride, 2-sulfobenzoic anhydride, tetraiodo-O-sulfobenzoic anhydride, tetrabromo-O-sulfobenzoic anhydride, tetra Cyclic sulfonic anhydrides such as chloro-O-sulfobenzoic anhydride and tetrafluoro-O-sulfobenzoic anhydride, chain phosphinic anhydrides such as diphenylphosphinic acid, cyclic such as 1-propanephosphonic anhydride Phosphonic anhydride, 3,4-diiodophenylboronic anhydride, 3,4-dibromophenylboronic anhydride, 3,4-dichlorophenylboronic anhydride, 3,4-difluorophenylboronic anhydride, 4 - iodophenylboronic anhydride, 4-bromophenylboronic anhydride, 4-chlorophenylboronic anhydride, 4-fluorophenylboronic anhydride, (m-terphenylboronic anhydride, 3,4,5- triiodophenyl boronic anhydride, 3,4,5-tribromophenyl boronic anhydride, 3,4,5-trichlorophenyl boronic anhydride, 3,4,5-trifluorophenyl boronic anhydride, etc. mentioned. Among these acid anhydrides, those having a cyclic structure are preferable in the present embodiment, and those having an unsaturated bond in the molecule are preferable. Among the acid anhydrides, maleic anhydride is particularly preferable from the viewpoints of availability and the fact that it has a cyclic structure and an unsaturated bond in the molecule.

3. Cyclic carbonate having an unsaturated bond The type of the cyclic carbonate having an unsaturated bond is not particularly limited as long as it does not impair the characteristics of the non-aqueous electrolytic solution of the present embodiment and the secondary battery using the same. You can choose from a variety of options. The number of unsaturated bonds is preferably 1-10, more preferably 1-5, and particularly preferably 1-3. Specific examples of cyclic carbonates having an unsaturated bond include vinylene carbonate, iodovinylene carbonate, bromvinylene carbonate, chlorovinylene carbonate, fluorovinylene carbonate, 1,2-diiodovinylene carbonate, 1,2-dibromo Vinylene carbonate, 1,2-dichlorovinylene carbonate, 1,2-difluorovinylene carbonate, methyl vinylene carbonate, iodomethyl vinylene carbonate, bromomethyl vinylene carbonate, chloromethyl vinylene carbonate, fluoromethyl vinylene carbonate, dichloromethyl vinylene carbonate, dibromomethyl Vinylene carbonate, dichloromethyl vinylene carbonate, difluoromethyl vinylene carbonate, triiodomethyl vinylene carbonate, tribromomethyl vinylene carbonate, trichloromethyl vinylene carbonate, trifluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, vinyl ethylene carbonate and the like. As the cyclic carbonate having an unsaturated bond, vinylene carbonate is preferable from the viewpoint of availability.

4. Halogen-containing cyclic carbonate The type of the halogen-containing cyclic carbonate is not particularly limited as long as it does not impair the characteristics of the non-aqueous electrolytic solution of the present embodiment and the secondary battery using the same. You can choose from a variety of options. Here, a halogen atom means a fluorine atom, a chlorine atom, a bromine atom or an iodine atom. Specific examples of cyclic carbonates having a halogen atom include iodoethylene carbonate, bromoethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, 1,2-diiodoethylene carbonate, 1,2-dibromoethylene carbonate, 1 ,2-dichloroethylene carbonate, 1,2-difluoroethylene carbonate and the like. As the cyclic carbonate having an unsaturated bond, chloroethylene carbonate and fluoroethylene carbonate are preferable from the viewpoint of availability.

5. Cyclic sulfonate ester As the cyclic sulfonate ester, there are no particular restrictions on the type of the cyclic sulfonate ester as long as it does not impair the characteristics of the non-aqueous electrolytic solution of the present embodiment and the secondary battery using the same, and various types can be used. can be selected. Specific examples of cyclic sulfonic acid esters include 1,3-propanesultone, 2,4-butanesultone, 1,4-butanesultone and ethylene sulfite. As the cyclic sulfonic acid ester, 1,3-propanesultone and ethylene sulfite are preferable from the viewpoint of availability.

6. Amines having an acetoacetyl group The amines having an acetoacetyl group are not particularly limited in type as long as they do not impair the characteristics of the non-aqueous electrolytic solution of the present embodiment and the secondary battery using the same. You can choose from a variety of options. Specific examples of amines having an acetoacetyl group include N,N-dimethylacetoacetamide, N,N-diethylacetoacetamide, N,N-dipropylacetoacetamide, N,N-dibutylacetoacetamide, N, N-ethylmethylacetoacetamide, N,N-methylpropylacetoacetamide, N,N-butylmethylacetoacetamide and the like. However, specific examples of these compounds are merely illustrations, and the present embodiment is not limited to these.

7. Phosphorus compound The phosphorus compound is not particularly limited as long as it does not impair the characteristics of the non-aqueous electrolyte of the present embodiment and the secondary battery using the same. Examples thereof include phosphines and phosphonic acids. Specific examples of phosphines include trimerylphosphine, triethylphosphine, triisopropylphosphine, triphenylphosphine and the like. Specific examples of phosphonic acids include dimethylphosphite, diethylphosphite, dibutylphosphite, diphenylphosphite, bis(2,2,2-trifluoroethyl)phosphite and the like.

The content of the additive is preferably in the range of 0.05% by mass to 50% by mass, and preferably in the range of 0.1% by mass to 30% by mass with respect to the total mass of the non-aqueous electrolyte. More preferably, it is particularly preferably in the range of 0.5% by mass to 20% by mass. By setting the content to 0.05% by mass or more, the effect as an additive, that is, a more stable film can be formed on the electrode surface. On the other hand, by setting the amount to be added to 20% by mass or less, it is possible to suppress an excessive decrease in the solubility of the electrolyte in the non-aqueous electrolyte in the non-aqueous solvent.

<Production of non-aqueous electrolyte>
The non-aqueous electrolytic solution of the present embodiment includes, for example, a non-aqueous solvent containing at least one of the phosphate esters represented by the chemical formulas (1) to (3), a difluorophosphate and/or a nitrate. It can be manufactured by adding a predetermined amount. At this time, it is not preferable that the difluorophosphate and nitrate become supersaturated and insoluble matter precipitates. Moreover, the non-aqueous solvent and the difluorophosphate and nitrate are preferably purified in advance to the extent that the production efficiency is not reduced, and the use of those with as few impurities as possible is preferred. When both difluorophosphate and nitrate are used as electrolytes, the order of addition to the non-aqueous solvent is not particularly limited and is arbitrary. When the non-aqueous electrolytic solution further contains additives, the order of the additives is not particularly limited and is arbitrary.

<Others>
Other conventionally known additives may be added to the non-aqueous electrolytic solution according to the present embodiment. In this case, the content of other additives can be appropriately set as required.

(Non-aqueous secondary battery)
Next, a non-aqueous secondary battery (hereinafter referred to as "secondary battery") according to the present embodiment will be described below with reference to FIG. FIG. 1 is a schematic cross-sectional view showing an outline of a secondary battery according to this embodiment.

The secondary battery of this embodiment can be applied to lithium ion secondary batteries, sodium ion secondary batteries, potassium ion secondary batteries, magnesium ion secondary batteries, calcium ion secondary batteries, and the like.

As shown in FIG. 1, the secondary battery has a stack in which a positive electrode 1, a separator 3, a negative electrode 2, and a spacer 7 are stacked in this order from the positive electrode can 4 side in an internal space formed by a positive electrode can 4 and a negative electrode can 5. It has a structure in which the body is stored. By interposing a spring 8 between the negative electrode can 5 and the spacer 7, the positive electrode 1 and the negative electrode 2 are appropriately crimped and fixed. A non-aqueous electrolyte is impregnated between the positive electrode 1 , the separator 3 and the negative electrode 2 . The positive electrode can 4 and the negative electrode can 5 are sandwiched between the positive electrode can 4 and the negative electrode can 5 with a gasket 6 interposed between them to join them together and keep the laminate in a sealed state.

The material of the positive electrode active material layer in the positive electrode 1 is not particularly limited, and examples thereof include a transition metal compound having a structure in which lithium ions can diffuse, or an oxide of the transition metal compound and lithium. Specifically, LiCoO ₂ ; LiNiO ₂ ; LiMn ₂ O ₄ ; a solid solution of Li ₂ MnO ₃ and LiMeO ₂ (Me represents _{a metallic element of Mn, Co or Ni); LiFePO 4 ;} LiMnPO4; _{Li2FePO4F ; LiNixCoyMnzO2} ( _{0≤x≤1 ,} 0≤y≤1 _, 0≤z≤1, _x + _y + _z = _{1 )} ; LiNixCoyAlzO2 (0≦x≦1, 0≦y≦1, 0≦z≦1, x+y+z=1); LiFeF ₃ ; oxides such as TiO ₂ , V ₂ O ₅ and MoO ₃ ; sulfides such as TiS ₂ and FeS sulfur; conductive polymers such as polyacetylene, polyparaphenylene, polyaniline and polypyrrole; activated carbon; radical-generating polymers;

The positive electrode 1 is formed by pressure-molding the above-described positive electrode active material together with a known conductive aid and binder, or by mixing the positive electrode active material together with a known conductive aid and binder in an organic solvent such as pyrrolidone. Then, it can be obtained by coating a paste-like product on a current collector such as an aluminum foil and then drying it.

The material of the negative electrode active material layer in the negative electrode 2 is not particularly limited as long as it is a material that can occlude (precipitate) and release (dissolve) metal ions. Examples include metal composite oxides and lithium metal. , lithium alloys, sodium metals, sodium alloys, potassium metals, potassium alloys, magnesium, magnesium alloys, calcium metals, calcium alloys, aluminum, aluminum alloys, silicon, silicon-based alloys, tin-based alloys, metal oxides, conductive materials such as polyacetylene soluble polymers, Li--Co--Ni based materials, carbon materials, and the like.

When using an alkali metal or an alkaline earth metal for the negative electrode, metal ions corresponding to the type of secondary battery are dissolved in the electrolytic solution as an electrolyte, and the metal deposited on the current collector during the charging process is removed. It can also be used as a negative electrode active material. In this case, only the current collector needs to be provided on the negative electrode side, which has the advantage of simplifying the battery configuration.

The metal composite oxide is not particularly limited, and examples thereof include Li _x Fe ₂ O ₃ (0≦x≦1), Li _x WO ₂ (0≦x≦1), Sn _x Me ¹ _1-x Me ² _y O _z (Me ¹ =Mn, Fe, Pb, Ge; Me ² =Al, B, P, Si, elements of groups 1 to 3 of the periodic table, halogen; 0<x≦1, 1 ≤ y ≤ 3, 1 ≤ z ≤ 8) and the like.

The metal oxide is not particularly limited, and examples thereof include SnO, SnO ₂ , SiO _x (0<x< ₂ ), PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O. _{4 , Sb2O5 , GeO, GeO2, Bi2O3 , Bi2O4 , Bi2O5 and} the _like .

The carbon material is not particularly limited, and examples thereof include natural graphite, artificial graphite, graphite borohydride, graphite fluoride, mesocarbon microbeads, pitch-based carbon fiber graphitized material, carbon nanotube, hard carbon, fullerene, graphene, and the like. .

For the negative electrode 2, a foil-like or powder-like electrode material can be used. In the case of a powder, copper is formed by pressure molding with a known conductive aid and a binder, or by mixing it with an organic solvent such as pyrrolidone together with a known conductive aid and a binder to make a paste. It can be obtained by applying it to a current collector such as a foil and then drying it.

In the lithium ion secondary battery according to the present embodiment, a separator 3 is normally interposed between the positive electrode 1 and the negative electrode 2 in order to prevent short circuit between them. Although the material and shape of the separator 3 are not particularly limited, it is preferable to use a material that easily passes the above-mentioned non-aqueous electrolyte, is an insulator, and is chemically stable. Examples thereof include microporous films, sheets, non-woven fabrics made of various polymer materials, their surfaces coated with glass, non-woven fabrics of glass fibers, and the like. Specific examples of polymer materials include polyolefin polymers such as nylon (registered trademark), nitrocellulose, polyacrylonitrile, polyvinylidene fluoride, polyethylene, and polypropylene. Polyolefin polymers are preferred from the viewpoint of electrochemical stability and chemical stability.

The optimum working voltage of the lithium-ion secondary battery of the present embodiment differs depending on the combination of the positive electrode 1 and the negative electrode 2, and is normally usable within the range of 2.4 to 4.6V.

The shape of the lithium-ion secondary battery of the present embodiment is not particularly limited, but in addition to the coin-shaped cell shown in FIG.

The secondary battery according to the present embodiment has sufficient flame retardancy and can exhibit excellent cycle characteristics and resistance characteristics. It can be used preferably. However, the lithium-ion secondary battery shown in FIG. 1 illustrates one aspect of the secondary battery of the present invention, and the secondary battery of the present invention is not limited to this.

Preferred embodiments of the present invention will be described in detail below. However, unless otherwise specified, the materials and compounding amounts described in the examples are not intended to limit the scope of the present invention.

(Example 1)
<Preparation of non-aqueous electrolyte>
Ethylene carbonate (EC, manufactured by Kishida Chemical Co., Ltd., lithium battery grade) and triethyl phosphate (TEP, manufactured by Tokyo Kasei Co., Ltd.) are mixed in an argon atmosphere dry box with a dew point of -70 ° C. or less. A non-aqueous solvent was prepared. The mixing ratio of EC and TEP in the non-aqueous solvent was EC:TEP=5:5 by volume.

Next, the non-aqueous solvent was mixed with LiPO ₂ F ₂ and LiPF ₆ as electrolytes. At this time, the concentration of LiPO ₂ F ₂ was adjusted to 0.5 mol/liter, and the concentration of LiPF ₆ was adjusted to 0.5 mol/liter. Thus, a non-aqueous electrolytic solution according to this example was prepared.
(Example 2)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=7:3 by volume. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for the above.

(Example 3)
In this example, only LiPO ₂ F ₂ was used as the electrolyte, and its concentration was changed to 1.0 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for the above.

(Example 4)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. Also, only LiPO ₂ F ₂ was used as the electrolyte, and its concentration was changed to 1.0 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 5)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for the above.

(Example 6)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. Also, the concentration of LiPO ₂ F ₂ and LiPF ₆ as electrolytes were changed to 0.8 mol/liter and 0.2 mol/liter, respectively. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 7)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. Also, the concentration of LiPO ₂ F ₂ and LiPF ₆ as electrolytes were changed to 0.2 mol/liter and 0.8 mol/liter, respectively. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 8)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. Also, the concentration of LiPO ₂ F ₂ and LiPF ₆ as electrolytes were changed to 0.1 mol/liter and 0.9 mol/liter, respectively. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 9)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. LiTFSI (Li(CF ₃ SO ₂ ) ₂ N) was used as the electrolyte instead of LiPF ₆ . A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 10)
In this example, a mixed solvent of ethylene carbonate and diethyl monofluorophosphate was used as the non-aqueous solvent, and the volume ratio of ethylene carbonate and diethyl monofluorophosphate was changed to 2:8. Furthermore, only LiPO ₂ F ₂ was used as the electrolyte and its concentration was changed to 1.0 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 11)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. Also, only LiNO ₃ was used as the electrolyte and its concentration was set to 1.0 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 12)
In this example, a mixed solvent of ethylene carbonate and diethyl phosphate (2-(2-(2-methoxyethoxy)ethoxy)ethyl phosphate) was used as the non-aqueous solvent, and ethylene carbonate and diethyl monofluorophosphate were used. volume ratio was changed to 2:8. Also, only LiNO ₃ was used as the electrolyte, and its concentration was set to 1.0 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 13)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. LiNO ₃ and LiTFSI were used as electrolytes, and their concentrations were 0.5 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 14)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. Also, LiPO ₂ F ₂ was changed to LiNO ₃ as an electrolyte. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 15)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. Also, as the electrolyte, LiPF ₆ was changed to LiNO ₃ . A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 16)
In this example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=2:8 in volume ratio. In addition, as electrolytes, LiNO ₃ at a concentration of 0.33 mol/liter, LiPO ₂ F ₂ at a concentration of 0.33 mol/liter, and LiPF ₆ at a concentration of 0.33 mol/liter were added to a non-aqueous solvent. Mixed. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 17)
In this example, a mixed solvent consisting of ethylene carbonate, triethyl phosphate and diethyl monofluorophosphate was used as the non-aqueous solvent, and the volume ratio of ethylene carbonate, triethyl phosphate and diethyl monofluorophosphate was 2. : changed to 4:4. Furthermore, only LiPO ₂ F ₂ was used as the electrolyte and its concentration was changed to 1.0 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 18)
In this example, the non-aqueous solvent was changed to a solvent consisting only of trimethyl phosphate (TMP). Also, LiNO ₃ , LiPO ₂ F ₂ and LiPF ₆ were used as electrolytes, and their concentrations were respectively 0.33 mol/liter for LiNO ₃ , 0.33 mol/liter for LiPO ₂ F ₂ and 0.33 mol/liter for LiPF ₆ . It was mixed with a non-aqueous solvent so as to have a concentration of 33 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 19)
In this example, a mixed solvent of propylene carbonate and triethyl phosphate was used as the non-aqueous solvent, and the volume ratio of propylene carbonate and triethyl phosphate was changed to 2:8. Furthermore, LiNO ₃ , LiPO ₂ F ₂ and LiPF ₆ were used as electrolytes, and their concentrations were respectively 0.33 mol/liter for LiNO ₃ , 0.33 mol/liter for LiPO ₂ F ₂ and 0.33 mol/liter for LiPF ₆ . It was mixed with a non-aqueous solvent so as to have a concentration of 33 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 20)
In this example, a mixed solvent of γ-butyrolactone and triethyl phosphate was used as the non-aqueous solvent, and the volume ratio of γ-butyrolactone and triethyl phosphate was changed to 5:5. Further, LiNO ₃ , LiPO ₂ F ₂ and LiPF ₆ were used as electrolytes, and their concentrations were respectively 0.33 mol/liter for LiNO ₃ , 0.33 mol/liter for LiPO ₂ F ₂ and 0.33 mol/liter for LiPF ₆ . It was mixed with a non-aqueous solvent so as to have a concentration of 33 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Example 21)
In this example, a mixed solvent of dimethyl sulfoxide (DMSO) and triethyl phosphate was used as the non-aqueous solvent, and the volume ratio of dimethyl sulfoxide and triethyl phosphate was changed to 2:8. Furthermore, LiNO ₃ , LiPO ₂ F ₂ and LiPF ₆ were used as electrolytes, and their concentrations were respectively 0.1 mol/liter for LiNO ₃ , 0.1 mol/liter for LiPO ₂ F ₂ and 0.1 mol/liter for LiPF ₆ . It was mixed with a non-aqueous solvent so as to have a concentration of 8 mol/liter. A non-aqueous electrolytic solution according to this example was prepared in the same manner as in Example 1 except for these.

(Comparative example 1)
Ethylene carbonate (EC, manufactured by Kishida Chemical Co., Ltd., lithium battery grade) and dimethyl carbonate (DMC, manufactured by Kishida Chemical Co., Ltd.) are mixed in an argon atmosphere dry box with a dew point of -70 ° C. or less, and A water solvent was prepared. The mixing ratio of EC and DMC in the non-aqueous solvent was EC:DMC=1:1 by volume.

Next, LiPF ₆ was mixed as an electrolyte in the non-aqueous solvent. At this time, the concentration of LiPF ₆ was adjusted to 1.0 mol/liter. Thus, a non-aqueous electrolytic solution according to this comparative example was prepared.

(Comparative example 2)
In this comparative example, the non-aqueous solvent was changed to a single EC solvent. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for the above.

(Comparative Example 3)
In this comparative example, a mixed solvent of EC and TEP was used as the non-aqueous solvent instead of the mixed solvent of EC and DMC. Also, the mixing ratio of EC and TEP was set to EC:TEP=9:1 in terms of volume ratio. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for these.

(Comparative Example 4)
In this comparative example, a mixed solvent of EC and TEP was used as the non-aqueous solvent instead of the mixed solvent of EC and DMC. Also, the mixing ratio of EC and TEP was set to EC:TEP=8:2 in terms of volume ratio. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for these.

(Comparative Example 5)
In this comparative example, a mixed solvent of EC and TEP was used as the non-aqueous solvent instead of the mixed solvent of EC and DMC. Also, the mixing ratio of EC and TEP was EC:TEP=7:3 in terms of volume ratio. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for these.

(Comparative Example 6)
In this comparative example, a mixed solvent of EC and TEP was used as the non-aqueous solvent instead of the mixed solvent of EC and DMC. Also, the mixing ratio of EC and TEP was EC:TEP=5:5 in terms of volume ratio. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for these.

(Comparative Example 7)
In this comparative example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=9:1 by volume. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Example 1 except for the above.

(Comparative Example 8)
In this comparative example, the mixing ratio of EC and TEP in the non-aqueous solvent was changed to EC:TEP=8:2 by volume. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Example 1 except for the above.

(Comparative Example 9)
In this comparative example, a mixed solvent of EC and TEP was used as the non-aqueous solvent instead of the mixed solvent of EC and DMC. Also, the mixing ratio of EC and TEP was EC:TEP=2:8 in terms of volume ratio. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for these.

(Comparative Example 10)
In this comparative example, a mixed solvent of EC and TEP was used as the non-aqueous solvent instead of the mixed solvent of EC and DMC. Also, the mixing ratio of EC and TEP was EC:TEP=2:8 in terms of volume ratio. In addition, LiTFSI was used as the electrolyte instead of _LiPF6 . A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for these.

(Comparative Example 11)
In this comparative example, a mixed solvent of DMSO and TEP was used as the non-aqueous solvent instead of the mixed solvent of EC and DMC. Also, the mixing ratio of DMSO and TEP was DMSO:TEP=2:8 in terms of volume ratio. A non-aqueous electrolytic solution according to this comparative example was prepared in the same manner as in Comparative Example 1 except for these.

(Combustion test of non-aqueous electrolyte)
First, samples were prepared by impregnating glass filter paper (trade name: GC-50, manufactured by Advantech Toyo Co., Ltd.) with the nonaqueous electrolytic solutions of Examples 1, 2, and 17 and Comparative Examples 1 to 8, respectively. Next, each sample was exposed to a flame of a gas burner for 1 second, and the sample was observed to conduct a combustion test. The combustion test was performed twice. Furthermore, based on the results of two combustion tests, it was determined whether the non-aqueous electrolyte was flame-retardant or combustible. The judgment criteria are ○ if the gas burner extinguishes the moment the flame is removed, x if it continues to burn even after the flame is removed, flame resistance if extinguished twice in a row, and other cases. was judged as combustible. Table 4 shows the results.

As can be seen from Table 4, in Comparative Example 1 using a mixed solvent consisting of ethylene carbonate and dimethyl carbonate and Comparative Example 2 using a solvent consisting only of ethylene carbonate, the non-aqueous electrolyte exhibited flammability. From these facts, it is inferred that the non-aqueous electrolyte exhibits flammability when a mixed solvent consisting of a cyclic carbonate and a chain carbonate or a solvent consisting only of a cyclic carbonate is used as the non-aqueous solvent. Also, in Comparative Examples 3, 4, 7 and 8, in which a mixed solvent of ethylene carbonate and triethyl phosphate was used, the non-aqueous electrolyte exhibited flammability.

On the other hand, even when a mixed solvent composed of ethylene carbonate and triethyl phosphate is used, the content of triethyl phosphate is set to 20% by mass or more with respect to the total mass of the non-aqueous electrolyte. It was possible to impart flame retardancy.

(Evaluation of cycle characteristics)
<Production of coin cell>
Coin-type lithium ion secondary batteries (coin cells) as shown in FIG. Electrochemical properties were evaluated.

That is, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Piotrek Co., Ltd.) cut into a diameter of 11.3 mm was used as the positive electrode, and glass filter paper (GC-50, Advantech Toyo Co., Ltd.) was used as the separator. ) was used. A lithium foil (manufactured by Honjo Metal Co., Ltd.) cut into a diameter of 13 mmφ was used for the negative electrode. Furthermore, the positive electrode, the separator, and the negative electrode are laminated in this order to form a laminate, and impregnated with the non-aqueous electrolyte solutions prepared in Examples 1 to 20 and Comparative Examples 5, 6, 9, and 10, respectively. It was sealed and a coin cell was produced respectively. All the coin cells were assembled in an argon glove box with a dew point of -70°C or less.

<Cycle characteristics and resistance characteristics of coin cells>
Each of the prepared coin cells was charged to a final voltage of 4.3 V at a charging current of 0.5 mA/cm ² in a constant temperature bath at 25° C. until the charging current became 0.15 mA/cm ² or less. After maintaining a constant potential at , the battery was discharged to a final voltage of 3.0 V at a discharge current of 0.5 mA/cm ² . It was charged and discharged 100 cycles by the current constant voltage method under these conditions. The discharge capacity and DC resistance after 100 cycles were comparatively evaluated. The direct current resistance was obtained by dividing the voltage loss obtained by subtracting the voltage at the end of charging and the voltage 3 seconds after the start of discharge by the discharge current. Table 5 shows the ratio of the discharge capacity and DC resistance of each example and comparative example when the value of comparative example 9 is set to 100.

As is clear from Table 5, the coin cells using the non-aqueous electrolyte solutions of each example containing a phosphoric acid ester that imparts flame retardancy had a higher discharge capacity after 100 cycles than each of the comparative examples. It was confirmed that the resistance was reduced. From this, it was confirmed that the non-aqueous electrolytic solution of each example and the lithium ion secondary battery using the same were excellent in practical use.

(Evaluation of coulomb efficiency characteristics)
<Production of coin cell>
Each of the non-aqueous electrolytes of Example 21 and Comparative Example 11 has poor oxidation resistance, and it is difficult to use an electrode such as LiNi _1/3 Co _1/3 Mn _1/3 O ₂ to which a high voltage is applied as the positive electrode. There are cases. Therefore, for these non-aqueous electrolytes, coin-shaped lithium ion secondary batteries (coin cells) shown in FIG.

That is, a copper foil cut into a diameter of 11.3 mm (manufactured by Nilaco Corporation) was used as the positive electrode, and glass filter paper (GC-50, manufactured by Advantec Toyo Co., Ltd.) was used as the separator. A lithium foil (manufactured by Honjo Metal Co., Ltd.) cut into a diameter of 13 mmφ was used for the negative electrode. Further, the positive electrode, the separator, and the negative electrode were laminated in this order to form a laminate, which was impregnated with the non-aqueous electrolytic solution of Example 21 or Comparative Example 11, and then sealed to prepare a coin cell. All the coin cells were assembled in an argon glove box with a dew point of -70°C or lower.

<Coulomb Efficiency of Coin Cell>
Each of the prepared coin cells was charged for 2 hours in a constant temperature bath at 25° C. at a charging current of 0.5 mA/cm ² to deposit metallic lithium, and then the final voltage was 1 at a discharging current of 0.5 mA/cm ² . 0 V to dissolve metallic lithium. It was charged and discharged 10 cycles by the current constant voltage method under these conditions. Coulomb efficiency after 10 cycles was comparatively evaluated. Table 6 shows the coulombic efficiency ratios of Example 21 and Comparative Example 11.

As can be seen from Table 6, in Comparative Example 11 using a non-aqueous electrolyte consisting of only LiPF ₆ as the electrolyte, the coulombic efficiency after 10 cycles was 16%. On the other hand, in Example 21 using the non-aqueous electrolyte containing LiNO ₃ and LiPO ₂ F ₂ , the coulombic efficiency was 79%, and compared with Comparative Example 11, the charge-discharge efficiency (cycle characteristics) was good. was confirmed. As a result, it was confirmed that a non-aqueous electrolyte using a mixed solvent of DMSO and TEP as a non-aqueous solvent and a lithium ion secondary battery using the non-aqueous electrolyte are also excellent in practical use.

1 positive electrode 2 negative electrode 3 separator 4 positive electrode can 5 negative electrode can 6 gasket 7 spacer

Claims (9)

A flame-retardant non-aqueous electrolytic solution containing at least a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent,
The non-aqueous solvent contains at least one of the phosphate esters represented by the following chemical formulas (1) to (3),
The electrolyte contains at least one of difluorophosphate and nitrate,
The flame-retardant non-aqueous electrolytic solution, wherein the content of the phosphate ester is 20% by mass or more with respect to the total mass of the flame-retardant non-aqueous electrolytic solution.

(wherein X ¹ to X ³ are each independently a hydrocarbon group having 1 to 20 carbon atoms; a silyl group having 1 to 20 carbon atoms; a range of 1 to 20 carbon atoms and a halogen atom; , a hydrocarbon group having at least one of hetero atoms or unsaturated bonds; Alternatively, X ¹ to X ³ are a hydrocarbon group having 1 to 20 carbon atoms; a silyl group having 1 to 20 carbon atoms; a hydrocarbon group having at least one of a halogen atom, a heteroatom, or an unsaturated bond; or at least one of a halogen atom, a heteroatom, or an unsaturated bond, wherein the number of carbon atoms is in the range of 1 to 20 , any combination of which are combined to form a cyclic structure, and Y ¹ and Y ² each independently represent a halogen atom.) 2. The flame-retardant nonaqueous electrolytic solution according to claim 1, wherein the mole fraction of at least one of the difluorophosphate and the nitrate is 0.1 or more with respect to the total number of moles of the electrolyte. 2. The flame-retardant non-aqueous electrolyte according to claim 1, wherein at least one of said difluorophosphate and said nitrate is an alkali metal salt. 2. The flame-retardant non-aqueous electrolyte according to claim 1, wherein at least one of said difluorophosphate and nitrate is a lithium salt. The phosphate esters include trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, diethyl monofluorophosphate, diethyl monofluorophosphate, ethyl difluorophosphate, ethyl dichlorophosphate, and diethyl phosphate (2 -(2-(2-methoxyethoxy)ethoxy)ethyl). 2. The method of claim 1, wherein the electrolyte further comprises at least one other electrolyte having an anion of BF ₄ ⁻ , PF ₆ ⁻ , N(CF ₃ SO ₂ ) ₂ ⁻ or N(SO ₂ F) ₂ ⁻ . Flame-retardant non-aqueous electrolyte. As the non-aqueous solvent, at least one selected from the group consisting of cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, lactone compounds, chain esters, nitrile compounds, amide compounds, sulfone compounds and sulfoxide compounds. The flame-retardant non-aqueous electrolyte of claim 1, further comprising: 2. The flame-retardant non-aqueous electrolyte according to claim 1, further comprising at least one of propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethylsulfoxide and tetraethylene glycol dimethyl ether as the non-aqueous solvent. A secondary battery comprising at least the flame-retardant non-aqueous electrolyte according to any one of claims 1 to 8, and a positive electrode and a negative electrode.

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